I notice a trend with a lot of D&D players, the longer they play. They start out doing the standard races, get bored with them, go through a phase of exotic characters (sometimes in an attempt to powergame, sometimes just looking for something new)-- minotaurs seem to be a popular choice in that regard. After that phase, they tend to settle down to making new and unique characters that have an lot of flavor behind them. It doesn't necessarily make the character very powerful-- in fact a lot of the time, I've seen players deliberately make the character less powerful because it fits better with the concept.
In that later category, I've got two concepts I'm really interested in playing, and I've seen many others that are fun. Here are my two:
An eco-terrorist druid. The character isn't stupid, so she doesn't go along and try to kill every lumberjack or cattleherd in existence; she picks her targets wisely. She's also high on the chaos factor, so, after the party has done everything they need to in the town, she may decide to prepare all 'Awaken' spells she can, and set the trees free. Or she may find the local sawmill and burn it down. The character would be aware of the need for party cohesiveness and wouldn't deliberately do things to screw the party over, but would certainly work towards the ideal of violently liberating plants and animals from under the yoke of humanity.
A wizard who doesn't appear to be a wizard. This evolved from a careful reading of the 3.5 rules for armor check penalty. Since a stilled spell isn't affected by the ACP, and neither are spells with no semantic components, this wizard would focus on those types of spells. He would also focus on spells that aren't obviously wizardy-- no fireballs or magic missles, but things like True Strike, Mage Armor, Bull's Strength, Charm Person, etc. would be his spells of choice. He would have to blow his first few feats on armor proficiency, martial weapon proficiency, and still spell. The wizard is trading some pretty powerful wizard spells for the sake of a little anonymity-- the mage is usually considered a big threat, and people go after him first, so he figures by appearing to be a roguish type, or some sort of weaker fighter, the enemy will think him less of a target, and allow him to be more effective.
I'm also in the process of trying to develop a paladin that doesn't act like a stereotypical paladin, but still maintains her calling in her own way. Does anyone else out there have some really interesting concepts that are a bit different than the normal, for flavor's sake? What are they like?