I always pick a character from a movie to play characters in my campaigns. For example, I might decide this dragonborn librarian is being played by Zorg from the Fifth Element, so he's going to talk with a slight west Texas twang.

Makes deciding what accent to use pretty easily, and gives me a canned personality to boot.

(My fallback for making the table regret talking to an NPC is Dick Van Dyke's terribly-accentented chimney sweep in Mary Poppins.)

I once did a campaign where all the bad guys where Gary Oldman in different roles