I'd honestly say the best free one...and I might get some stick about this, but it is free and works rather well:
Movie Maker 1 and 2 by Microsoft
If you have Windows ME, XP then this program should already be on your PC within the Programs, Accessories folder. If you have XP, you can also download Movie Maker 2 which has some extra features within it.
The bad thing about it though, is it only allows you to export in the Windows Media Video format (WMV) so thats a bit of a downer and is a bad move I think for Microsoft because it is okay at editing movies.
There is another free one which I've heard is good, though I don't have the name to hand. I'll try and post it later on
Hope this helps