Premiere Pro and Final Cut are the obvious top two choices and are generally regarded as the best and most used. However, these programs cost a LOT of money. If you want to invest that kind of cash in a program, go for it, however I expect that a lot of posts in this thread will tell you to torrent it.
That is certainly an option, but if you are trying to purchase a program legitimately, I suggest looking into an academic license for either Premier Pro or Final Cut. Basically it's a student/teachers way to get the program a bit more affordably.
Another option is to check out Adobe Premiere Elements. I use this quite a bit for my personal editing and works pretty well. If you are not doing anything too crazy in depth, it works just dandy. If you're looking for the full shabang and you think you are going to be using every editing tool available, then stick with the pro options.