I usually create folders for designers and place those folders inside my brushes folder. That helps me keep track of where they came from and who made them. I also have a folder for "unknwon' people and for my own.
When I DL'd Zip'd files I make the folder for them and place them directly into it. Then I unzip them and delete the zipped file. It is really easy to keep track of them since they are already in a folder with the designers name.
Another thing I've done in the past (haven't done it recently) is that every time I downloaded a new set of brushes I'd open up an 8.5x11 white paper and stamp a sample of each brush onto the page and write the collection/set name on the page. Then i'd print it out and put it next to the computer in a folder for quick referrence. That way I'd know what brush set to load.

just my way of doing it though.