If you want to crop a video quickly and easily, Free Video Cutter will do the job
Free Video Cutter is a tiny program does exactly what is says, with no frills or extras. It can import and export MPEG4, DivX, WMV, MOV, FLV or MP3 formats (including conversions), with minimal fuss.
Simply open a video file, wait for it to load and then choose the part of the video you want using the markers. The precision of the crop depends on your Free Video Cutter import options - the higher the precision the longer it takes to import, but the more accurately you can edit.
Free Video Cutter has very few options - you can choose the output format, but there are no quality settings. There is also no sound in Free Video Cutter, so you have to make your cut just using images. Sound will be kept for your edited video, you just can't hear it in the app itself. Ironically, you can set the output to MP3 and convert the sound from your video!
Free Video Cutter would be improved if you could import DVDs too, but is nevertheless a very easy to use program ideal for cutting video for YouTube etc.