1. Flv Converter: This tool helps to converts YouTube videos to various formats like .AVI, .MOV(for MAC), 3GP(for mobiles). This tool is designed by SGRA Corporation as a part of vixy project. Link: http://vixy.net/flv_converter
2. Videodl(beta): VideoDL is a quick AJAX application that allows you to download online video into your computer. It supports top 3 video sites - YouTube, Google Video, and Break.com. Simply copy the link of the page with video and paste it into the textbox. Click "Get It!" and follow the instruction. After you have saved the files into your harddrive.
3. Feeling tea(beta) : This tool works fine with GoogleVideo, Youtube, Putfile.com, Blip.tv, Break.com , ThatVideoSite, Current.tv , Vidilife.com, Videocodezone.com, Videocodes4u.com, Sharkle.com, Streetfire.net, Revver.com and Lulu.tv
Friends, if you know more tools that does the trick.. do post it here for otheres to refer