In case you haven't noticed by now, CreepyPasta is just horror stories and urban legends that are usually based around something in pop culture.
Personally, Hypno's Lullaby, while disturbing, is one of the better ones I've read since its a poem. Most CreepyPastas are really dumb and poorly written. If you want a nice satire on the Sonic.exe creepypasta, check out Yuriofwind on youtube. I would link, but he's got a potty mouth
He's done a number of videos pretty much bashing creepypastas. I love it.