MovieStamper lets you permalink and tag your favorite movie scenes. For instance, check out the timestamps for The Departed or Office Space. (Oh, and I know you’re eventually going to click on the boobs tag, so here you go. NSFW.)
It’s all a bit proof of concept right now, but if people start using it in earnest, it could be a fantastic resource.
Update: Looks like the Moviestamper site is no more. The URL now links to a parked domain with ads so I removed the link. (thx, jeff)