Heck, if you're at work and want to be really 'discrete' (ie. can't be talking out loud for obvious reasons), I've also just recently tried gaming with
Mibbet, which is just a simple web IRC chat platform. Can't do die rolls (sadly), but you can set up nicknames (Player names) and have separate chat threads (OCC, IC, etc.)
You can set up a channel and people can join in.