I've been on the internet for a long time, and USENET newsgroups had always been the best source of quality information that I had found. The quality of the information for the "lurker" and quick response time to posted questions had always been quite good. Lately, though, I've come to appreciate the value that "moderation" systems can have on an open-posting forum. In brief, when a posting happens, people graced with the ability to moderate review the post and assign a rating or upvote/downvote to it. The users can then filter what postings they read based on this rating, or on more selective sites, the rating determines whether the posting stays on the system at all.
Whenever I'm browsing Slashdot, I'm consistently surprised by how many useful/interesting postings I'm presented with when browsing with a "filter" level of 5. Obviously I'm not alone in liking this site, as Slashdot is semi-notorious for the "Slashdot Effect", in which sites that are referred to in a headline posting tend to go down or be overwhelmed with requests due to the sheer number of people coming in from Slashdot.
Most people know what Slashdot is; on a more unique level, there's Everything2. This site is like a cross between a universal knowledgebase and an adventure game; people post "writeups" to it, on the topics of, well, everything. Well-received postings increase one's XP (eXperience Points), and after gaining so many points, the user reaches another level, in which they have more capabilities in what they can do on the site, such as voting themselves. This system is quite effective at eliciting the users' best efforts in writing--I've found an amazing amount of interesting postings/articles there. Though the site can tend to be a bit elitist, one could say the people who've put a great deal of time and effort into this fine site deserve to be.
(My stuff on Slashdot. My stuff on Everything2.)