Hi, I'll assume that you're interest in Go since you've visit this page. Some believe that play wei-qi can improve your critical thinking skill. This is because you have to "read" out the game before hand. Please don't be scare by this "read" thing. To be honest with you, learn how to play wei-qi is just as easy as learn how to tie your shoes. But learning and mastering is two different things. And lucky for us, no one can ever master wei-qi! (phew~ my confidence coming back~!)
If you're want to learn how to play wei-qi, below are some very good sites.
Website for wei-qi's lessons
http://senseis.xmp.net/ (recommend for new player!)
http://goproblems.com/ (problems solving)
http://www.playgo.to/interactive/ (Lesson)
http://www.361points.com/
http://www.gokgs.com/ (play online)
Feel free to contact me if you have question about wei-qi, and if I don't know the answer, I will find out about it for you if my time allow me. Hope to see you in the World Of Go.