I will second Adobe Premiere Elements 12. It is a slightly lesser version of Premiere Pro. Cost is only $99.99 from Adobe. iMovie is still a great program to use as well once you get a feel for it. Good for basic editing. Premiere Elements will be easy to learn and gives your some additional tools and plugins to work with that iMovie does not have.
I think once you learn PE, you will fall back on iMovie for simple edits as I do.