George Shepherd's Windows Forms FAQ contains an aggregation of questions and answers from a variety of online resources (newsgroups, forums, et al). This site is definitely worthy of a position on your bookmarked sites list.

Duncan (and a few other MS bloggers) have mentioned the new PInvoke.net site that surfaced recently. This looks to be promising and I, like everyone else, look forward to seeing how the development community contributes to this. If you're wondering...