If you're not familiar with what 'rule 34' is, basically a back in the day quote that goes as follows: 'Rule #34. There is porn of it. No exceptions.' People realized soon after getting on the Internet that finding adult entertainment of any nature was possible thanks to the weird and creative genius of humankind. Want to find dinosaurs fucking cars? That exists. What about Jesus taking it in the butt? Hell yeah that's around.
Anyway, Rule34.xxx is a site that exploits this simple fact of the Internet by trying to archive and tag multiple sources of weird or strange pornography. There are a lot of cartoons and anime/hentai scenes, with quite a big focus on characters from comics being made into sexy slut nuggets. Rule 34 certainly does a good job at getting their hands on all of this material and as far as I'm concerned, if you need to source some weird or wonderful sex, this place probably has.