I'm a sucker for:
- thieves with 1d6 HP, so they aren't third-rate fighters.
- thieves with thief abilities that aren't so awful that they are poor thieves, as well.
Over at Hill Cantons there is s variant thief that's pretty interesting.
A Revised Thief Class for B/X or LL
Good stuff, I don't know if I'd use it (I might do my own, if I ran B/X or LL) but it's very good.