MTV's MTVmusic.com, a very clean, very simple, good looking site full of music videos and only music videos. Lots of older, classic stuff, too, like Dire Straits' “Money For Nothing.” The site looks good and, in our limited testing, works great. And like Hulu, MTV also (smartly) lets you embed their videos on your blog, MySpace or Facebook profile, Tumblr, etc. (see below). It also has the requisite "social" functions like comments, rating up/down, etc.
While the design is clean, there's also room for one or two ad units per page -- currently house ads for other music videos -- and presumably MTV will be able to sell post-roll, pre-roll, or pop-over ads, too.