Just archive them on CD and organize them according to use...dirtmaps, skies, metals, wood, tiles, etc...or according to project type (i.e., sci-fi, creature/character skin, etc.). Then when you get to that stage in a project where you're ready to start texturing, assuming you have a general idea of what you want your scene to look like, grab a bunch of files and store them in your project's source files folder or wherever you want.