I've been using Videopad lately.... it seems to work okay. Very similar to Windows Movie Maker, with a few extra functions, and can handle HD well, where as WMM cant.
If you're using a Mac, Apple iMovie isn't too bad. Final Cut Pro is better... Adobe premier is the way to go if you can afford it....
Edit: heres an example of something I put together in VideoPad:
http://www.youtube.com/watch?v=06y9rQ8SUP8Just mucking around really with a couple of days worth of footage. I didnt bother to render the final product in HD as my computer is old and takes FOREVER to do movie editing. Im happy with the result of a couple of hours of dicking around. Its no BBC Oceans, but it atleast shows that it can do what you're after
- also apologies for the camera angle being too low on the gun... the jerry rigged mount was falling apart during this dive and wouldnt hold the gopro in position.