twinspires.com and xpressbet will be offering wagering on the derby. twin spires is not yet up and running, but it should be by the time the derby arrives. Here is a paragraph from the article in bloodhorse.
TwinSpires (
www.twinspires.com) is the official ADW service for its family of racetracks, as well for the Kentucky Derby and Kentucky Oaks. TwinSpires, a wholly owned subsidiary of CDI, offers wagering on races from Churchill Downs, Santa Anita, Gulfstream Park, Fair Grounds Race Course, Pimlico Race Course, Lone Star Park, Golden Gate Fields, Laurel Park and other popular racing venues. TwinSpires is headquartered in Mountain View, Calif., and operates a wagering hub in Oregon.