It's hard to actually find a game to play over the internet, often its a group a friends doing it because getting together at one place can often be pretty hard, especially for people with kids. There's plenty of programs you can use, all of which take a bit of practice to actually DM with, but with the right group (just like in RL) it is awesome. Fantasy Grounds 2 is very nice if your DM has the spare time and sheer willpower to put everything into it, once the groundwork is done its very smoothly and has a great feel.
But if you're having trouble finding a group, I'd suggest a Play by Post site, there's alot of them out there. Though as zen5887 said, they're a very slow way to play, with people usually posting once a day (some games are faster 2-3 day, others are 2-3 posts per week). However this usually attracts a different type of crowd. The slowness of the games, and being able to write things out makes it much easier to roleplay properly. I used to post on DnDOG a fair bit, really good site with some excellent staff and on the whole great community.