So you've got pen & paper role playing games, you have live action LARPS, you have MMORPG (just say M-Morp-er-ger), you have tabletopping, you have play by mail, play by email, interactive storytelling, theater sports, lone hack and slash CRPG, and then you have Yathzee. Also with dice.
Recently I stumbled on what I guess are two of the leading products. The first is Fantasy Grounds, which has a pretty high wow looks factor. If you have to make your own virtual handouts for the game, or fill in scores of sheets however you might start to think otherwise. But it has a steady fanbase, and its well tested. The other contender I found is Battlegrounds, also with pretty nifty screen shots, and a slightly friendlier pricing scheme. It's less specifically fit for role playing games, but it does feature a big selection of art packs, games and adventures, also many for free. Once you have bought a GM client licence, that is.
If you're intrigued, and live far from the civilized world, you may also have a look at the RPG Virtual Tabletop wiki. And see if it's for you.
Image cropped gratefully from Battlegrounds