For freeware, definitely Windows Movie Maker. It's very user-friendly too as far as I remember, I was able to make my own custom effects and titles simple enough. Things like picture-in-picture was possible which was pushing WMM's limits, and there's lots of effects packages folk have put together to enhance WMM for people's needs.
I now use Sony Vegas for my vids but I don't forget my days using WMM, and how I tried to make the most with what I had.