Hmm... I think I'd make a female human Chaotic Good fighter/thief... no, reformed assassin dualed to fighter, but with special shadow armor that gives her bonuses to some of her thief abilities so that she wouldn't be a sucky dead-end thief. She would be a friend to any PC, talking to him/her extensively, and a possible romance for a male PC of any race or class. I would also make it possible to betray her and change her alignment in a creepy, nasty way, so she could really fit in any party.
Oh, wait, I just remembered, I really am making an NPC like that! ***SHAMELESS PLUG ALERT***
Xero--Heheh, Lehtinan's actually the scumbag you help Hendak kill.