Just go to google and type "sex".
Since you are lucky click on "i'm feeling lucky"
Enjoy!
Now you are bored and you want more site, so this time type "sex" but do a standard request, then click on "similar" for the first link.
hint try:
related:
www.pornhub.com/ "sex"
You can try the same thing with "porn" or "xxx"
conclusion:
Napster: ok
Pirate bay: ok
Google: not ok