The Wikipedia article about gripe sites:
http://en.wikipedia.org/wiki/Gripe_site

Another list of gripe sites (along with some helpful information about starting your own):
http://www.webgripesites.com/

An interesting piece about how at least some lawyers are realizing the pointlessness of threatening or suing the operators of gripe sites, noting that most of them are completely legal:
http://www.techdirt.com/articles/20090405/1832594397.shtml

From the other side of the fence, a company trying to sell a service to shut down gripe sites (worth a read):
http://www.hostingdude.com/internet_complaint_sites/stop_internet_complaint_sites.htm

Another interesting article about gripe sites in general:
http://www.associatedcontent.com/article/60685/gripe_sites_when_something_sucks_post.html

http://farmersreallysucks.com/editorialtakedown1.shtml where the site admin takes the Farmers lawyers to school in his response to their C&D
http://farmersreallysucks.com/editorialarentfoxsucks.shtml same site.  The admin takes the lawyers to task for being idiots.
http://farmersreallysucks.com/editorialgetafirstlife.shtml again, same site.  Easily the most hilarious spoof on a C&D ever.  It was written by lawyers for a company called Linden Labs who knew the fast track to infamy was threatening the little guy.  They took the ball and ran it back for a positive PR touchdown.  I with other companies were this enlightened.

Cheers mate,
-really sucks admin