Here's an idea that I just got from Scott Hargis that can help cover your plane rental if you are going up to shoot an aerial shot. Send out an e-mail to all your regular customers and every listing agent that has a high-end listing in your area. Offer to shoot their current listings while you're up. Notice that you can offer to shoot landmarks and lakes, not just current listings on the market. Try and get a long shoot list so you are making money the whole time you are up in the air!
Update 4/29: Peggy (in the comments) raises a good question on what are some tips for shooting from an aircraft? There are many readers that shoot this way. There have been many discussions in the PFRE flickr group over the years on aerial photography. Take a look here for a list of aerial photography discussions.
Oh and BTW, if you are in the San Francisco/Oakland area and want a great aerial shot of your listing or your favorite landmark Scott is going up to shoot aerials. Contact Scott (510.551.3647) before 8PM Monday 4/29 and get on his shoot list.