Final Cut Pro is an excellent upgrade from Apple's iMovie. Where iMovie's prebuilt templates can be limiting, Final Cut allows for manual controls of pre-loaded graphic templates, and a wider selection of thematic elements. While expensive right away, this one time purchase means that the program will 'pay for itself' quickly, and updates to the program will always come free; therefore making this option more economical in the long run against it's Adobe competitor.
Final Cut Pro can be purchased from the App Store here.