Nowadays almost all quite decent mobiles have multimedia support to play videos in 3GP format. The next step is to convert all the videos on your PC directly to that 3GP to enjoy them as much on your PC as on your mobile, showing them to all your friends.
So you can convert the following formats to 3GP: AVI, DivX, WMV, ASF, PSP (Photoshop), iPod Video (to pass it from a portable device to your mobile), VOB, MOV (Quicktime) and MPEG4.
You will then have the latest and newest videos on your mobile.