YouTube
If you've not already stumbled across this site you must have been living in the wilderness for the last 10 years, but there's no denying the unlimited procrastination potential of YouTube. If you want to chill and listen to some music, there are millions of videos for that (provided of course that they've not been removed by copyrighters). If you want to watch videos that are oddly intriguing for no real reason at all, then there are thousands of these too, such as this one. And if you want to watch fat people hurting themselves, then there is no better place. YouTube has more videos than you could ever watch in a lifetime, but a true procrastinator would still try.
To get just a small impression of the potential of this site, check out this video.