This app will allow you to download video's from most streaming video sites (youtube, redtube plus 100's more) and has a really nifty feature that allows you to convert said video into the file type of your choice - very handy for Mobiles, PSP/DS etc...

Freeware, too.

Download here, open the video you want to download in your browser, copy the link into the programme, and that's that.

Have fun.