There are lots of tools for saving articles to read later, but not so much for videos around the web, unless you're devoted to just one site. Radbox clips and saves videos from YouTube, DailyMotion, Vimeo and other spots for leisurely watching.
Radbox works through a simple bookmarklet that you click whenever you're on a page with a video you want to save. The basic compatibility list reads "YouTube, Vimeo, Metacafe, DailyMotion, CollegeHumor, Hulu, Blip.tv, Megavideo, TED, etc." In my own testing, I liked the way Radbox lined up and played my selected videos with a note about when I saved them, but found that, about half the time, I'd need to click on a video and bring it up on its original site (i.e. click embedded YouTube clips and view them on YouTube) to ensure the Radbox bookmarklet picked up the video for sure.
Radbox is a free service, requires a quick sign-up to use.