Virtually every national car rental firm allows this. Some have hefty drop-off fees, some don't. You can look at a variety of firms if you click on the "Travel Reservations" link in the green navigation bar on this page.
If you look at the Gear-up forum or click on this link, you can look at some other rental car information.Also, do you have a site or link on here where I can get info on this?
Mark