groups.yahoo.com/ group /refactoring. A group for discussing refactoring.
groups.yahoo.com/group/extremeprogramming A group for discussing XP. There's a lot of discussion unrelated to refactoring, but refactoring is one of the key practices in XP.
www.refactoring.com. Martin Fowler's site, associated with Refactoring . He has most of that book's catalog online, along with contributions from others.
www.industriallogic.com. Joshua Kerievsky's corporate site. He's working on a book, Refactoring to Patterns , and has interesting articles and games as well.
www.xp123.com/rwb. In general, my site is focused on XP, and the rwb area is devoted to this book. You'll find source code for the larger examples, refactoring- related articles, and pointers to refactoring challenges others have proposed.