You downloaded big AVI files from your camera. My Canon PowerShot S5 IS for 3 minutes of video produces AVI file with aprox 500MB in size. Lets say you have about 5 or 6 of such AVIs files spread around. It is really easy to compress them. One nix command. Here it is:
find command searches for all files with AVI extention and for each of them executes command after —exec switch (which is ffmpeg -i input file -b bit rate). Curly brackets stand for currently found file.