Firefox: Whether Rickrolling left you permanently scarred or you're just a cautious link clicker, VideoSurf is an add-on for Firefox which not only lets you peek at a thumbnail of video links but gives you useful information about them.
VideoSurf will convert video links you find via Twitter, Yahoo, YouTube, Google, and FriendFeed. Instead of seeing just a plain link, you see a thumbnail and a mini story board of frames from the video. The sample image above is from a search on Twitter for "healthcare". Check out the video below to see VideoSurf in action.
VideoSurf is free and works wherever Firefox does.