If you are keen to buy or sell websites and blogs these forums are good places to watch every day. Now and then a really good bargain pops up so make sure if you are serious that you keep a careful lookout or you may miss a deal.
The best site in my opinion is SitePoint -
http://www.sitepoint.com/forums/forumdisplay.php?f=56
These two are good as well.
http://forums.digitalpoint.com/forumdisplay.php?f=52
http://www.webmaster-talk.com/websites-sale/