Harrah's has recently announced that they will add a HORSE event to the WSOP, likely before or after the Main Event. With the $50,000 buyin, this event stands a very good chance of exceeding the Main Event in first place prize money.
Many people have complained that the WSOP event schedule focuses too much on NL Hold'Em, and this event was created in response to that. For those not familar, HORSE is a mixed game, with levels of Hold'Em (limit), Omaha, Razz, Seven Card-Stud, and Stud Eight or Better (Stud hi/lo). Because you have to be a very skilled player to do well in all of these games, expect to see only the top names competing in this event.
If you'd like to play HORSE,
Full Tilt is the only site you can give it a try at, since they are the only site that offers Razz. However,
Poker Stars has play-money versions of Omaha and the Stud games, so you can get a feel for the games there as well.
Right now
Full Tilt only offers HORSE in tourney form, but a ring game version is on the horizon...