The immensely popular MetaCafe which was rumored to be in acquisition talks back in December, has just launched their Facebook application. While I prefer YouTube over MetaCafe, this application has robust integration. You can view the most popular videos overall and within your network as well as search through all the videos on MetaCafe.
Additionally, you can come up with your own custom MetaCafe channels. One thing that seems to be missing from this application is the upload feature. I would also like to see the ability to display your custom MetaCafe channel within your Facebook profile. That would provide more integration into the social side of Facebook. Aside from that this is a relatively simple yet highly functional application. If you are in to MetaCafe videos, go grab the MetaCafe application.