Discord is a service similar to Skype, but designed for gaming communities.
It can be used from a browser or a downloadable client.
A lot of gaming communities have started using it and I decided to make one for our LEGO MMO wikis.
If you'd like to try it out, here's an invite link: 
When you first join, you will need to be granted the permission to send messages, you can ask a bureaucrat to do so in the #unverified channel.