http://www.5z.com/tucsongo/book (Go Seigen games)
http://www.go4go.net/v2 (commentary by Alexander Dinerchtein)
http://www.gobase.org (not updated much)
http://www.gogameworld.com (commentary by from other sources, which are then translated)
http://www.internetgoschool.com (contains free samples here)
http://www.kiseidodigital.com (Go World archives DVD)