The
TinyChat resource works very quickly and easily - it will create a room for you and you can just dive in. It also works in conjunction with Twitter, and invites you to use your Twitter name. However, the downside is that if you use your Twitter name it takes control of your account and posts a message on your behalf to say you're chatting, which I think is really out of order. There are also no admin controls, so if someone unsavoury should manage to get in there's little to be done about it, short of leaving and creating a new room.
However, for a chat between friends that were on Twitter at the same time, a quick DM to let them know the room details and it could be quite useful. Don't know if the room every closes though - it may do once everyone leaves or it might sit around for ever! A friend has offered to babysit it for an hour to see what happens....