There's a great thread for Chameleon builds on the CharOp forum... which is down right now. I'll link it to you later. I actually want to play a Chameleon sometime, but unfortunately finding an online group that will allow it and plays when I'm free is the hard part

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Anyway, there are a few ways you can go about the first five levels for Chameleon. There are more, and you can check the CharOp forum to make sure I've gotten them all.
Just so we know what we're shooting for here, if you want to attack well, you really want either at least +16 BAB or slightly less BAB with Divine Metamagic. If you're playing in a lower-power campaign, that's not necessary, of course. The first class level should give you your Bluff and Disguise as class skills (Able Learner makes them class skills for the other four levels as well), and the other four levels should be used to pick up the abilities you want before going into Chameleon. You can use a class that doesn't have one of either Bluff or Disguise at level 1 and choose another class that does later, but I won't explore that here. Just be aware it is a viable option.
Don't forget you get Able Learner, so class skills from any class you have become class skills for all classes you have. This makes skill points per level more important than the class skill list, as long as you make sure one of the classes has the class skills you want.
The following recommendations are for characters who will be getting the full 10 levels of Chameleon. The other good stopping point for Chameleon is 7 levels, and that changes things a bit.
First Level: Getting The Skills
Ideally, you want a class that gets Bluff and Disguise as class skills at level 1. Here are the classes that meet that criteria along with what else they give you (warning: I probably missed some):
Core:
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Bard: 6+int skill points, Inspire Courage or Fascinate 1/day, UMD as class skill
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Cleric with Trickery Domain: 2+int skill points, another domain, Turn Undead, level 1 divine spellcasting
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Rogue: 8+int skill points, Trapfinding, Sneak Attack +1d6, UMD as class skill
SRD:
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Cloistered Cleric with Trickery Domain: 6+int skill points, more class skills, Knowledge and another domain, Turn Undead, level 1 divine spellcasting - basically like normal Cleric, but better since you'll be gaining proficiencies anyway.
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Feat Rogue: Like Rogue, but you trade +1d6 Sneak Attack for a Fighter bonus feat.
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Human Paragon: 4+int skill points, Adaptive Learning (useless with Able Learner, but GOODIES come at levels 2 and 3), any 10 skills as class skill
Completes:
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Ninja: 6+int skill points, Wis to AC, +2 Will Saves (Ki Power), Sudden Strike +1d6, Trapfinding
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Sorcerer with Draconic Heritage (Silver): 2+int skill points, level 1 arcane spellcasting (True Strike, etc)
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Warlock: 2+int skill points, Eldritch Blast 1d6, 1 least invocation, UMD as class skill
PHB2:
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Beguiler: 6+int skill points, Trapfinding, 1st level arcane spellcasting (note: Armored Mage doesn't apply to non-Beguiler spellcasting), UMD as a class skill
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Dragon Shaman with Silver Dragon totem: 2+int skill points, 3 Draconic auras (+1)
There's a lot of good options here. Since you mentioned you want trapfinding and want to use your 1st level to pick it up, Rogues, Feat Rogues (I personally prefer the feat to sneak attack), and Ninjas are best. Beguilers really don't have much to offer for the build. The Clerics provide you with Turn Undead, allowing you to take the deliciously strong Divine Metamagic. You don't even have to use it with Persistent Spell; Quicken Spell can be good enough. Also, with Persistent Spell and Divine Metamagic, you can cast a Find Traps that lasts all day. Granted, it doesn't give you the ability to disable them, but the magic ones at least can be dispelled.
While Human Paragon and Warlocks aren't as good for dipping, they get really good if you take a few more levels. Human Paragon gets a bonus feat at level 2 and a +2 increase (not bonus) to any ability score at level 3. This can combine with your Chameleon ability boon bonus to achieve really high ability modifiers (great with Charisma for Divine Metamagic! or Strength, I guess, or a casting stat). Warlocks get the ability to take 10 with UMD checks at level 4, along with a few more invocations and Detect Magic at will.
The Other Four Levels: Abilities Galore
The other four levels are a great time to pick up any other abilities you want. While the possibilities are really limitless, here are some ideas. Remember, more skill points is nice because of Able Learner, and full BAB progression is great as well.
PHB:
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Barbarian 4: 4+int skill points. Full BAB progression, 2/day Rage, Uncanny Dodge at level 2. Dipping one level gives you 1/day Rage.
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Fighter 4: 2+int skill points. Full BAB progression, 3 bonus feats. Good if you can use PHBII, because you can pick up Weapon Focus, Weapon Specialization, and Melee Weapon Specialization for +3 attack and +4 damage. It's like you've just doubled your Combat Focus!
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Monk 2: 4+int skill points. 2 bonus feats, Evasion, Improved Unarmed Strike at level 1, Flurry of Blows at level 1, Wis to AC at level 1.
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Paladin 4: 2+int skill points. Full BAB progression, Turn Undead, Cha to Saves at level 2, Smite Evil 1/day at level 1, and some other minor perks.
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Ranger 2: 6+int skill points. Full BAB progression, A bonus feat, Track at level 1, and a favored enemy at level 1. If you really need Endurance as an extra feat, you can take 3 levels.
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Rogue 5: 8+int skill points. This is one where there's no bad place to stop. Level 5 gets you another Sneak Attack die (or bonus feat if using the feat rogue), level 4 gets you Uncanny Dodge, level 3 is a Sneak Attack die or bonus feat, and level 2 gets you Evasion.
SRD:
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Human Paragon 3: 4+int skill points. +2 ability score, unrestricted Bonus Feat at level 2, and you get 2/3 spellcasting which means you don't fall behind too much at low levels.
Completes:
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Hexblade 3: 2+int skill points. Full BAB progression, Mettle, Cha to Saves vs. arcane spells at level 2. You can get a familiar with Hexblade 4. Hexblade's Curse isn't worth it unless you use the unofficial revision suggestions from the Hexblade designer, in which case it could be a decent bonus.
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Ninja 5: 6+int skill points. Another die of sudden strike, another use of Ki and Great Leap at level 4, a die of Sudden Strike and poison use at level 3, and what is effectively Swift Invisibility at level 2. I'm not sure this is worth it, but maybe you're a Leap Attacker that really want the Great Leap. Like the Rogue, there's really no bad place to stop.
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Scout 4: 8+int skill points. A bonus feat at level 4, +10 move speed and +1 AC while skirmishing at level 3, uncanny dodge at level 2, and skirmish and trapfinding at level 1. You want Scout 5 for another die of skirmish damage, but sadly this class doesn't have Bluff or Disguise as class skills. Could be useful if you plan on progressing this after your Chameleon levels.
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Spellthief 1: 6+int skill points. +1d6 Sneak Attack and trapfinding. If you want +1 saves vs. arcane spells, you can take another level although I don't think it's worth it.
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Swashbuckler 3: 4+int skill points. Int to precision damage, plus Weapon Finesse at level 1.
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Warlock 4: 2+int skill points. Take 10 on UMD checks, an extra invocation at levels 2 and 4, and Detect Magic at will at level 2. A lot of the Least Invocations are very useful even at higher levels, so this is pretty powerful.
PHBII:
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Dragon Shaman 5: 2+int skill points. +2 Draconic Aura, Breath Weapon at level 4 (really only good with the Entangling Exhalation feat from Races of the Dragon), Draconic Adaptation at level 3, and some other perks. I'm not sure the +2 Draconic Aura is worth it at higher levels.
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Duskblade 3: 2+int skill points. This is really only for arcane channeling.
If you have Dragon Magic and Races of the Dragon, a 1-level dip into Dragonfire Adept and Entangling Exhalation also works. You'll also get a Least Invocation and the Dragontouched feat, which gives you some minor perks and qualifies you for draconic feats.
There's a ton of options here. It might be a bit overwhelming, but just think about what abilities would be fun to play with and go from there.
After Chameleon:
After your Chameleon levels, you'll have 5 more levels to play with. You can dip some more and get more fun abilities (but watch out for multiclass penalties!), or just progress along a class to get its higher level abilities. If you plan on doing this, you might want to take more of that class during your first five levels.
Chameleon's BAB can qualify you for Prestige Classes, so take a look at prestige classes that have BAB requirements. If your other classes give you spellcasting or abilities, you can qualify for a wider range of PrCs.
Arcane Strike is a feat in Complete Warrior that is incredibly powerful for fighters with arcane spell slots. You can expend multiple spell slots on the same turn, and while the attack bonus doesn't stack, the damage does. Unfortunately, it requires 3rd level arcane spellcasting, which Chameleon doesn't qualify us for. Taking levels in Wizard or something is kind of wasteful due to its low BAB, and other gish classes like Hexblade and Duskblade have spellcasting that progress too slow to be of use. However, there is a prestige class in Complete Arcane called the Suel Arcanamach, which gains 3rd level casting in 4 levels. You may have to work with your DM to adapt the PrC though, and its requirements basically require DM approval. Now, there's two ways of doing this. You can either delay your Chameleon progression so you get Suel Arcanamach 4 by level 18 and take Arcane Strike (or even delay it so you can get it by level 15), or you can take all 10 levels of Chameleon but be forced to use your Chameleon floating feat for Arcane Strike. Suel Arcanamach is a great way to cap off the last few levels in your build, but of course, there are other options.