Ooh! I can help out. I'm currently playing an Arcane Disciple at the moment, actually.
Arcane Disciple was a variant Cleric from the recent Spellcasting issue of Dragon. The idea behind it is that it's a Cleric that chooses to revere Magic itself as a force above any other- higher than even the gods. Rather than getting Domains and Domain spells, the Arcane Disciple has a class ability called "Arcane to Divine"- every level, they choose one Arcane spell to be added to their spell list, and is forever a Divine spell for them. The only limitations are that it has to be at least one level lower than the highest level spell you can cast. So, at 20th level, you'll have all of the Cleric spells, as well as 20 arcane spells of your choice, from 0-level to 8th-level, that you cast as Divine spells. It's an interesting concept, although, like all of the other variant class, kinda sucks.
After all, your Hit Die decreases to a d6. You lose proficiency with Heavy Armor. You get less spells per day, since you no longer have Domain spells- although that's minor. You also don't get any Domain granted powers. However, since the class bases itself more on Magic than upholding alignments or religions, you lose the ability to Turn or Rebuke Undead.
On the upside, though, you gain more skill points, and have a much better selection of Class skills. The spells, over time, will be much more advantageous than if you had Domain spells, because you can choose whichever ones you want, and generally the majority of Domain spells are already on the Cleric spell list. So you'll be getting a lot more spells that you'd want to use. Plus, all of the spells on the Magic Domain are already considered to be on your spell list, meaning that you can cast Identify, Antimagic Field, and even Mordenkainen's Disjunction (at a high enough level, that is) without having to use up one of your Arcane to Divine spells. Oh, and another huge plus is that you gain Bonus feats like a Wizard- so you get an extra Metamagic or Item Creation feat at levels 5, 10, 15, and 20.
The main disadvantage of choosing your own Arcane spells every level is that they have to be a level behind all of your other spells. So you have to wait until level 7 to get Fireball, or Fly, or whatever, and you'll never be able to get Time Stop or Wish or Meteor Swarm- but hey, you're a lot better off than if you were just a normal Cleric.
When I started making this character, I soon realized that somethign about it just didn't seem balanced with the normal Cleric. Most of it balanced out, but it was still lacking something. I talked to my DM, and we decided it would be balanced if they still had the ability to Turn or Rebuke Undead- it doesn't quite fit the character concept, but the class just isn't balanced without it. So we stuck that back in. Aside from that, the class has been great for me.
So far, I'm an 11th-level Lawful Neutral Arcane Disciple of Wee Jas (the goddess of Death and Magic). The Arcane spells I've taken were Arcane Mark and Touch of Fatigue (0-level), Magic Missile and Ray of Enfeeblement (1st-level, both have served me very well), Touch of Idiocy and Alter Self (2nd-level), Haste and Vampiric touch (3rd-level), Dimension Door and Greater Invisibility (4th-level), and Feeblemind (5th-level). I've got maxed out Knowledge: Arcana, Knowledge: Religion, Spellcraft, Use Magic Device and Concentration (all of which are Class skills, and then some, for the Arcane Disciple). I've got Scribe Scroll, Craft Wondrous Item, Craft Magic Arms & Armor, Silent Spell, Still Spell, Reach Spell, and I'm planning on getting Forge Ring next level. All in all, the class has been working really well for me. I really like the character concept.
(Also, it'd be a funny thing to do to your PCs- have them come across a treasure horde with Divine scrolls of Magic Missile and Fireball. They won't know what the heck is going on!)
If you've got any more questions about the Arcane Disciple, and want to talk to someone who's used one, Email me or something.
