Sony Vegas Pro 8.0b = Effective for heav duty editing, relatively easy to use, most recommended. Run a google search on it, its a great program and i use it for all my youtube stuff.
Adobe After Effects CS3 = Best for professional grade work, extremely effective, difficult to get the hang of, but worth a try. Tutorials at
www.videocopilot.net
hope these help, or you could always use the free (yet embarrasingly crappy, impossibly to look like you have any editing skill at all with this hunk of garbage) Windows Movie Maker.