The Something Awful Forums (http://forums.somethingawful.com ) or SA forums are the messageboard of comedy site Something Awful, and the origin of the Let's Play concept. Originally a community surrounding the site's comedy-oriented front page, it's grown to one of the largest and most popular forums on the internet, with the front page taking a backseat in popularity. SomethingAwful charges $10 to register an account, and is actively moderated, a form of curation that largely ensures that content remains fresh and useful, and ensuring that a lot of the drama found on other forums and sites stays out.
The Let's Play concept originated from a thread on Something Awful called "Let's Play Oregon Trail." The original poster posted screenshots of the classic game and asked for input from people replying to the thread about what to do in the game. He did what they told him to do and posted screenshots of the results, resulting in everyone in the thread effectively playing the game together (hence, "Let's Play"). The concept was a huge hit and immediately spawned many similar threads, so many that the Let's Play subforum was created for them. Let's Play is a subforum of Something Awful's "Games" forum, and is the premiere source on the internet for quality LPs, especially hybrid and SSLPs. The LP forum is heavily integrated with the LP Archive and nearly all of the archive's 1500+ completed LPs came from SA, dating back to the origins in 2006. The SA forums also gave birth to LPix.org, a custom image hosting site specifically for SSLPs, with its own uploading tool.