Here are some Go sites you may find useful:
KGS Go Server - play Go on the Internet, against people from all over the world. Also a great tool for reviewing games and teaching Go.
American Go Association - the official national organization of U.S. go players
The Interactive Way to Go - web-based tutorial for learning Go
Sensei's Library - online resource for studying Go
Go Problems - online database of interactive Go problems that can be solved within your browser
A Kid's Guide to Playing Go - recommended by one of our younger players
Videos about Go: