well, ive never played as a player, but being a DM for ~6 years for the same group i have certainly created a NPC's that are/were favorites of mine.
my first villain was (and still is) great:
Hizor is a yuan-ti gifted lizarman psionic warrior, who specialized espionage and assassination for "the order." his hit and run tactics, combined with superhuman athleticism and stealth make him a fierce (and frustrating) foe indeed. early on in the campaign he murdered one of the PCs when their guard was down, and ever since they have both hated, and feared him.
my personal favorite:
derik korbis: the only thing this devil-may-care citystate external security agent loves more than women is brutal violence. he is well known for his habit of wading in to combat with no shirt and a fine cigar, and seems to take great pleasure in such daring acts. this ranger, sporting quick hands, a magical repeating heavy crossbow, and a bad attitude is a favorite ally of the PCs, both for his snake-pliskin-meets-james-bond like demeanor, and his ability to lay down a preposterous amounts of suppressive fire (he has, on more that one occasion, sunken an enemy boat with adamantine bolts).
you guys have some classic moments - saving the day and killing yourself all in one shot, PC vs. PC ... nice.