A good example: http://www.iiiiiiii.com/
Warning: Auto playing audio.
A bad example: http://www.scribd.com/
Warning: YouTube clone where 2chan clone would suffice.
Speaking of 2chan: there seems to be a misconception with western web designers that login screens (and thus, registration screens) are essential. Well:
Registration sucks. Login sucks!
Please give me this:
4chan FAQ entry on tripcodes
And not this:
digg register, very simple for a western registration form
I'm yet to see an application not involving money where registration is essential.