Hello...
You found the place to get the answers.
There are a couple different styles of online games. The first is in this forum, which is a play-by-post. This is a "stickied" or main thread in the RPG forum.
The DFRPG LFG is the 'looking for gamers" area. This is where you can post either on-location or online games that need players or a GM or whatever.
The Undertown game uses a chatroom style game. We use a 'private' chat (just paid for by one of the members but anyone can show up). We have one that records an archive so we can go back and save games. Then we use another room to roll and chat.
There is a virtual tabletop game in beta that looks promising, and it will allow you to load maps, roll, set up a site chat, etc. our GM is on the beta group but it will take a bit to get it up and going.
Some players use skype.
The biggest challenge is rolling and recording them. But the online, typing only games do take more time. Getting everyone together is a challenge, but we've been running the Undertown game for almost 2 years all in chat.
You can see if anyone is looking for gamers in an established game, or try to start your own. This is a good place to start.
Its also a good place to ask questions and look for ideas.
Take a look at some of the PbP games, and some of the Resource collection.
A few of us have posted our cities to be used as a start if you would prefer to have a framework to build on.
What are you trying to do./ the answer is here......