Skype is excellent, I've been using it for well over a year now and am very happy. I"ve also paid for skype out which allows me to call land lines cheap and the quality is fantastic.
Recently skype added video beta which also works really great if you have a web cam. I like it since my parents can see thier grandchildren even though they live 1000s of kilometres away.
EFL Geek
EFL Geek: ESL & EFL in Korea