Whitney Elizabeth Houston (Brown) 1963-2012

 Genre appearances included...

Rodgers & Hammerstein's Cinderella (Fairy Godmother / performer: "Prologue", "Impossible", "It's Possible", "Finale Ultimo", "There's Music in You")
The Preacher's Wife (Julia Biggs)
The BodyGuard (Rachel Marron / performer: "Queen of the Night")

 Note: The BodyGuard is not really genre, but it's use of footage from the classic 1926 film Metropolis as well as the Maria-Robotrix-influenced costume prominently featured in the video for "Queen of the Night" and the film itself make it worthy, IMHO, of inclusion.

Check out...
Whitney's Official WebSite
A cool FanSite

Other actresses to play Fairy Godmother in Rodgers & Hammerstein's Cinderella include Celeste Holm [1965] and Edie Adams [1957]

Other actresses to play Julia Biggs include...
Actually, in the previous version of this film, The Bishop's Wife [1947], the character was named Julia Brougham and played by Loretta Young.

Marsha A Hunt

Though born in America, Marsha A. Hunt found fame and success in Europe.
She first caught the public's eye in the London stage production of Hair where her striking appearance lead to fashion modeling (including British Vogue) and her singing voice lead to studio and on-stage backup singing!

A solarized graphic of Marsha was used as the iconic image on the original theatrical poster

She also had co-starring roles in a number of films, including several genre flicks.
Marsha has written a number of well-received novels, an autobiography, a memoir about her battle with breast cancer and is currently writing a book about Jimi Hendrix.
She still performs on stage in England, including a play based on one of her novels and directed by her daughter.
Trivia: She was romantically-involved with Mick Jagger, and had a child with him.
Jagger's song "Brown Sugar" was written about his affair with her.

Genre appearances include...
Sender (Nurse Jo)
Howling II: Your Sister is a WereWolf (Mariana)
Dracula A.D. 1972 (Gaynor)

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)

Ashanti Shequoiya Douglas

Another singer / actress with several genre credits, and a fair number of other film / tv appearances as well.
Ashanti is a superb soprano, and a competent actress, with an enthusiasm for action stunts.

Her genre credits include...
Resident Evil: Extinction(Betty)
Muppets' Wizard of Oz(Dorothy Gale)
Buffy the Vampire Slayer "First Date" (Lissa)

Check out...
AshantiMusic
Ashanti Daily (FanSite)

Other actresses to play Dorothy Gale include...
Tin Man: Grace Wheeler, Zooey Deschanel, Alexis Llewellen, Rachel Patee (Dorothy at various ages)
The Dreamer of Oz: Courtney Barilla (Dorothy Gale / Dorothy Leslie Gage [the real-life inspiration for the character])
Return to Oz(1985): Fairuza Balk
The Wiz: Diana Ross
The Wiz (Broadway): Stephanie Mills
Journey Back to Oz; Liza Minelli (daughter of Judy Garland)
Off to See the Wizard: June Foray
Return to Oz(1964) Susan Conway
The Wizard of Oz (1939) / Lux Radio Theatre "Wizard of Oz": Judy Garland
The Land of Oz aka The Scarecrow of Oz: Maryeruth Boone
The Wizard of Oz(1925): Dorothy Dwan
Dorothy and the Scarecrow of Oz: Marcia Moore
The Wizard of Oz(1910): Bebe Daniels

Samantha Tamania Anne Cecilia Mumba

Another singer turned actress, Samantha debuted in the most recent film version of H.G. Wells' classic novel, The Time Machine (and was one of the few good things about the flick)!
She's also done two reality tv series Dancing on Ice, and Get Your Act Together.

Genre appearances include...
Loftus Hall
3 Crosses
Cross aka Shifter (Ishka)
Boy Eats Girl(Jessica)
Nailed(Sapphire)
The Time Machine[2002] (Mara)
Barbie as Rapunzel(performer: "Wish Upon A Star")
Evolution(performer: "Baby, Come On Over"

Check out...
Samantha's MySpace page
A FanPage

Beyoncé Giselle Knowles (Carter?)

Both an award-winning single-named singer and a talented actress, Beyonce has done relatively little genre work, but what she has done has been attention-grabbing!
Curiously, though her non-genre acting had been in "serious" films like Cadillac Records and DreamGirls, her genre movie work had only been in comedies...until Obsessed!

Genre appearances... 
Obsessed (Sharon Charles)

Austin Powers in Goldmember 
 (Foxxy Cleopatra, also performed song on soundtrack)
The Pink Panther
(Xania, also performed songs on soundtrack)
Pepsi Commercial "Dare for More: Gladiators"
(Gladiator, also performed song)

Check out...
The Official Beyonce HomePage
BeyonceWorld (FanPage)