Ward Cunningham's wiki (he invented wikis -- the c2.com one was the first one and is still active) has a lot of discussion, especially but not exclusively about patterns (Ward was very involved in the start of the whole idea of design patterns, as well as agile programming and quite a few more things;-). You can start here for example. It's not as coordinated and structured as you desire (actually pretty chaotic at times;-) but it can be really instructive to follow all the back-and-forth debates.
