Nina Munteanu at Darwin's Paradox has written a couple of thought starting articles for beginning writers. The first titled, Common Pitfalls of the Beginning Writer - Part 1: Characters, offers some suggestions for creating interesting characters and includes a character checklist.
I've been listening to Up in Honey's Room on CD during my commute to work this week. Written by Elmore Leonard, the novel is an excellent study of characters and how to develop them and illustrates Ms. Munteanu's points perfectly. Characters in the story include an Oklahoma law man, German Nazi's, a German butcher, a femme from Kentucky, a bbq entrepreneur from Georgia, and a few others. When read aloud the characters come alive.
The narrator adds a lot to the subtle nuances of speech that defines Leonard's distinctive characters, but the author deserves 90% of the credit. Without the written word, the spoken word would not have the same effect. When listening to the narrator, it's easy to determine who is speaking based on the accent, vocal mannerisms, clothing being worn, moral traits, etc.
With this in mind, I'm going to read my own writing aloud and record it on a tape recorder with the goal of improving my own characters. Wish me luck!