ClipGrab can download videos from many different video sites. These include YouTube, Vimeo and Dailymotion. You can find more information about the supported video sites here.
ClipGrab can convert downloaded videos to MPEG4, MP3, OGG Vorbis, OGG Theora and WMV. It also supports downloading the original FLV or MPEG4 videos without conversion.
With ClipGrab, however, it is very easy to download videos on your PC or Mac and then transfer them on your mobile device.