KeepVid allows you to download videos from almost all popular video sharing networks (Youtube, GoogleVideo, etc.). You can download videos either via Keepvid.com OR use provided browser bookmarklet to grab videos directly from the webpage.
- Download videos from: Youtube, GoogleVideo, Break.com, Dailymotion, Blip.tv, Groper, Current TV, and dozens of other video sharing websites.
- Browser bookmarklet: Download videos directly from the video webpage.
UPDATE: MakeUseOf put together a list of best sites for watching TV shows. Download it here. Enjoy!