Depends on what you need to do.
Add a intro and transitions? Windows Live Movie Maker. Downside is your videos DO have to be on your C drive and not on a network.
Something with a little more oomph but still user friendly? Adobe Priemere Elements
Something professional? Adobe Priemere Pro
I know there are others out there, but those are the 3 I have experience with. Priemere Pro is like Photoshop, it's either got to be your hobby or you go somewhere to learn how to use it properly.