As should be clear from our many posts about it, QuickTime Pro offers some pretty nice basic editing features for $30. Nonetheless, you might think there is room for another low-end video editing application for the Mac, precisely because QuickTime Pro is so centered around the MOV container and Apple favored codecs like H.264. In a cross-platform world much of the video you might run across, and want to edit, won't be in Apple favored formats. Though QuickTime Pro may be able to handle many of these through separate codec plugins, SimpleMovieX has the advantage of having native support for the common MPEG and AVI formats, which allows you to edit, split, and merge AVI files encoded with DivX. The SimpleMovieX developers have a comparison page that lays out the differences to QuickTime Pro. SimpleMovieX is well worth a look for simple video editing needs, particularly without the need for transcoding.
SimpleMovieX is the same $30 as QuickTime Pro, but unlike the latter a demo is available for download.