Just to name a few:
BG1 - Portalbendarwinden, Melinkamp, Albert and Ruffie, the kid with the drowned cat, and the chanters in Candlekeep garden (God, I can still hear them in my head), Silence from the shop of Silence ("Is ye friend or is ye dead?")...
BG2 - pretty much all citizens of Athkatla, from the street kids ("My mamma works in the Copper Coronet. What's a slattern?"), to the noblemen/women ("I don't usually speak to the likes of you, but hello"), to prostitutes ("Well if ye wants to go strapping with this nab, you'll first have to give up the socket-money."). Also Dradeel ("You have lots of time for reflection while waiting for the endless waves of bad-doggie werewolf monsters that chew your toes while you're asleep."), the beholder from Shauagin city, the Lesser demonlord from the underdark ("It is most amusing, daughter darkling, the child of Bhaal has murdered you.").
IWD2 - the captain's mom (the way she talks... Ravel, is that you?), the two mercenaries in the pallisade boasting about their vermin extermination activities ("We made five gold!" PC: "I can pull five gold out of my stool."), Boghrob the giant ("They'se da ones wat smashed up the ice castle and they killed me brudda...").
PS:T - Dhall, the black abishai, the elderly hive dweller, Reekwind, Adahn, O, Ingress, the Starved dogs barking, the floating skull near the portal in Curst Gone (I also love Coaxmetal, but I don't think he counts as a minor character).