I can also recommend Chess.com - I thought it would just be somebody who'd snapped up the domain and ran with it, but it's actually done really well. You can play all sorts of games (and tournaments) for free, from two weeks per move to two minutes for the entire game. There're also a bunch of learning resources, including enough free stuff to get by (in combination with the links carroters gave you ldo) if you don't wanna become a paid member (I'm not a paid member, so my endorsement is of chess.com as a free site).