Reddit has a new dedicated video site called Reddit.tv for clips that have become popular on its main page, as well as on its "sub-Reddit" categories. It consists of a simple video player that streams in clips, along with a playlist that lets you jump around. Nearly all of the ones I saw were from YouTube, but there were a few from Vimeo as well. There's also the option to send the video you're watching as a Twitter message, which links back to the Reddit.tv player. Users of Ffwd's Twitmatic will feel right at home.
The site is a little more than just a video playlist though. It's also linking to the source discussion on Reddit, as well as highlighting the top-rated user comment. It's a tad sparse considering the richness of a good Reddit comment thread (which can be several hundred comments long), but for casual users who don't know much about Reddit, it's a nice way to get them in the door.
Competitor Digg has had its own video subsection since late 2006, which simply takes all the popular videos from its various categories and puts them on one page; however it doesn't have a unified player. The closest it comes is by letting users play the videos right on the site as an overlay if the video creators have allowed for embedding off-site.