My favorite build has become what I like to call the "toolbox." Sort of a jack-of-all-trades character, that can do a lot of things with some proficiency, but not too many with extreme masterful skill. Granted, this is definitely no tank, and I'd rather run than solo in most cases, but it makes for a really solid support role.
Race: Human
Rogue (3) / Scout (3) / Wizard (3) ECL 9 (rogue at 1st level, then evenly in succession to ECL 9)
Make sure to get your mobility, two weapon fighting, and shot on the run feats in that equation (without recalling the math shot on the run might end up taking more than ECL 9 worth of feats, but gear up for it!)
The way this character works is an Intelligence rogue with Dexterity as the secondary skill. The intelligence score grants you so many skill points, especially with rogue at 1st level, that there's really nothing you can't at least take a shot at doing. Intelligence also works in conjunction with the wizard class, so there's no shortage of casting ability either. But don't focus on the direct damage spells with this build, you want the supplemental spells, Expeditious Retreat (add that with the scout's skirmish and difficult terrain movement), Obscuring Mist (now you see me, now you don't, and yes that's my sword in your back), Detect Secret Doors, Comprehend Languages, Disguise Self, and others like these are really more useful to this build than a fireball. I've even gone as far as to make the Wizard specialization to exclude Evocation, but that stretches it just a bit.
The greatest part about this build is that the Scout Skirmish and Rogue Sneak Attack damage bonus stack, so long as you meet both requirements of non-detection or flanking, and movement prior to attacking, you get double the damage, and when in situations where one or the other must be excluded, you can usually manage to get the other one to apply.
I prefer to focus on my ranged abilities with this build, the only down side is that none of these classes and human are not proficient with the longbow, so to do your best with basic equipment you need to burn a feat. This got me thinking in the long run, and decided to seek an even more deadly ranged weapon for this build. After all, if I have to burn a feat to use a weapon, make it damned powerful: the Heavy Repeating Crossbow!
Scout the hall...
Hide at the threshold... (sneak attack achieved)
Step out.. (skirmish achieved)
Fire.. Fire.. Fire... (yes, they felt that)
Step to other side... (shot on the run)
So what has anyone else thought up?