Ella, Louie, Sinatra, Ms. Holiday... They're all great! Jazz is my favorite genre of music to sing most of the time :) Occasionally I get an a mood to belt out something different and I might do Evanescence or something like that...but Jazz as a general rule suits my voice the best.
Love, love, love Jazz! I got Loe and the Nastys' album off of iTunes--and they're a pretty good modern jazzy band. :) Jazz meets Katamari Damaci.
EDIT: Found this--it's one of my current favorite songs.