We have a small oil stain on our concrete garage floor. We sealed this concrete several years ago with a roll on type sealer (not very heavy duty). We tried to remove the stain first by washing it with soap and water, then Windex, then CLR. Well, the stain is still there. Any suggestions?
Thanks.

None of the products you mentioned are good at removal of oil from concrete.
If the stain has been there a long time, you may have a very difficult time of it.

Check the first 3 links here for other methods that work if it's not been there for a long time:

http://www.google.com/search?hl=en&q=remove+oil+stain+concrete+garage+floor&btnG=Google+Search

Hey! Check out OIL GONE EASY's HOME & DRIVEWAY S-200 (http://www.oilgoneeasy.com/index.php?main_page=product_info&cPath=65&products_id=180). This is the best oil stain remover that I have come across. I am sure that it will work great until the last drop of motor oil disappears from your drive.
Here is a link that might be useful Best Oil Stain Remover, Driveway Cleaner, Remove Concrete Stain, Bilge Cleaner, Oil Spill Cleanup - Oil Gone Easy (http://oilgoneeasy.com)

Concrete is porous so the stain is in not on the concrete. Once there it can be very hard to completely remove since it can reach down into the thickness of the conrete. I have not used the product mentioned above but it appears worth trying.