I found that archiving freebies into folders named after the creator or website helped me...since I tend to get multiple textures from one source anyway. For example, I have a folder called "Lemog" with all my lemog textures in it. Or sometimes I'll add a readme.txt in a folder with information about some odd freebies that don't necessarily fit perfectly in a category. It helps to put the web address somewhere, either as the folder's name or a note inside the folder. I wish I had thought of this system earlier though as I do have a handful of textures I can't use because I can't remember where I got 'em from. :/