a few tips for you:
Post an ad in the Petfinder classifieds. Go to www.petfinder.com
and click on the link to Classifieds on the top of the ad.
Ask for an adoption fee (maybe $20-$50). This can help keep away people that want cats for experimentation or for dog fighting bait. (I know it's disgusting and unthinkable, but it's reality). Please, never put "Free to a good home" on anything, it's just asking for trouble. If you find a great family and choose not to charge the fee, they'll be even happier.
See if you can include the litter box, litter, food bowls, toys, poop scoops and anything else you aunt may have had for the cat. It's easier on the cat to have some of it's own things and it's good for the new owners to have equipment to start out with (if they don't already).
Put an ad in your local papers, up at the grocery stores and anywhere else these things can be posted.
on your ads, put as many Personal things that you can about the cat. Is he/she a cuddler, good with kids, dogs, other cats, does he/she do well alone and therefore be good for a working family?
Most important of all, don't lie. You can put a cat in alot of danger if you tell someone that he's sweet and he's really not all the time. They should know what they're getting up-front.
I answer a "owner surrender" line for the rescue that I foster for and I've been through alot of this. If you want more advise or need help, please feel free to PM me. I'll do anything I can to help you out.