The "P-P-P-Powerbook!" prank. Someone wants to sell their Powerbook, no longer having a need for it. The first person to respond turned out to be a 419 Scam. Instead of blowing him off, the seller, with a little inspiration from other Goons, string the scammer along. The end result has to be seen to be believed.
Their absolute thrashing of Reddit, for even allowing child porn to be posted there (the site's founder knows about it, but refuses to do anything about it, something that can't even be said for 4chan.). They even reported it to the FBI. Their reactions,on the other hand...
On 2/12/2012 a thread was made in GBS calling attention to the fact that though /r/jailbait had been closed, child porn was still prevalent on the site. Within hours, thanks to sending off a large list of offending subreddits and information to various news sites, facebook... anyone who would listen really, they were successful in getting the admins to finally put a stop to the child porn and close down (and ban) any subreddits dedicated to posting pictures of underage girls.
"If you want to show your children that love — like bravery and every other emotion — takes all forms, take them to see Rango again. At least that won't make them look at their friends' families (or their own) and think they're inherently flawed. However, if you can tell me that you want to send the message to your children that there's only one way a kid can be loved, then by all means take them to see Mars Needs Moms, and remind me not to let my future offspring play with yours."