WatchVideo is a Qt application (but also comes with a command-line version) to play, download, rip or convert (to Ogg) videos from Bliptv, Break, CaracolTV, CineGratis24h, CollegeHumor, Current, Dailymotion, Metacafe, Sapovideos, TheOnion, Vimeo, YouTube, and others. 

What makes WatchVideo special is that besides being able to download videos from many video sharing websites, it can also rip/convert and play them, either using an external player (such as Totem or VLC) or you can use the internal player (mplayer - this is an experimental feature in the latest version). The rip/convert/play actions can be set to occur once a video has finished downloading which is a real time-saver feature. WatchVideo also comes with NotifyOSD notifications for Ubuntu users.