depends on how serious you area about editing, can't justify spending thousands of $s on editing if your not that serious about it, but if you are serious about it, ya get finnal cut pro and a power mac and you'll be set.
Everybody so far has said Premiere Pro, and i agree. But if you don't want to spend so much money on software you could go w/ Roxio Videowave. It's cheap and it's sure not as good as Adobe, but it gets the job done and saves you a bundle.
I have Final Cut Express, saved hundreds of dollars, and have no complaints. I'm not sure what the differences are now between Express and Pro, but it's worth checking out.