I use Adobe Premiere Pro. You can get it on its own, or you can get the Adobe Suite which also has Photoshop, Audition, and Aftereffects.
Naturally- these ain't cheap, but they're of great quality.
I wouldn't call them exactly simple- it's more like Chess: easy to get the basics- but you can easily spend a lifetime trying to finangle all the bells and whistles in any reasonable manner.