Despite the seeming stranglehold that no-limit hold'em has on the poker industry (and culture) these days, there are, indeed, pockets where other poker games are holding their own. For instance, I was gratified to see pot-limit Omaha maintain about a 40% market share in the poker room at the Grey Eagle Resort and Casino in Calgary, Alberta. (Typical PLO situation — it's 60/40, including its market share in a Canadian poker room.)
In the online space, PokerStars certainly offers the most options for playing non-hold'em variants. After the aforementioned PLO, our most popular poker variant is actually a cocktail of poker games called "8-game.