Alicia Keys

Yet another singer (albeit a Grammy-Award winning performer) turned actress, Alicia made a cameo in an episode of Charmed, then hit the screen shooting as a lesbian assassin in Smokin' Aces.and received kudos for her dramatic ability in Secret Life of Bees!
UPDATE: Props to Ms. Keys for yet another Grammy win! Way to go, lady!

Genre appearances include...
Quantum of Solace[22nd Eon James Bond]
(co-performer w/ Jack White: main theme "Another Way To Die")
Hollywood Homicide(performer: "A Woman's Worth")
Dr. Dolittle 2(performer: "Rear View Mirror")
The Backyardiagans"Mission to Mars" (Boinga's Mom / performer: "Almost Everything is Boinga")
Smokin' Aces(Georgia Sykes)
Charmed"Size Matters"

Check out:

Alicia's Official Site
Alicia Keys Online (the #1 Source for ALL Things Alicia, according to them)