Will said:
What would be cool is a 'edge on fighting' feat... say, +1 dodge bonus if your off-hand is unoccupied (no buckler nor spells)
That is, fencing, which has the advantage of showing a smaller profile, but doesn't allow two-handed attacks or two weapon fighting.
Similar to the old AD&D2 concept of "one-weapon style" specialization, which gave an AC bonus.
How-evah, I'd be inclined not to do that in 3.5, for the simple reason that TWF now has "off-hand defense," which gives an AC bonus, and it seems that too many styles would be edging in on the same niche.
Some other concepts might be an initiative bonus, or even a concept that I've played around with a few times, the "stepping lunge," whereby, essentially, you threaten an area within a 10' reach, at some cost (like, an AC or attack penalty, or both), to represent the quick, highly extended lunges of some fencing styles.
There's also disarm-focused stuff, since there is a natural advantage to disarming if you have a hand free (you get the weapon).
What I'd stay away from: Damage bonuses (infringes on big-weapon and two-weapon niches), AC bonuses (infringes on sword-and-board and, to a lesser extent, two-weapon niches).