I will be flying into Heathrow in August and need to rent a car in Oxford for siteseeing. Any suggestions on the best way to get to Oxford from the airport and where I can rent a car (hopefully very close to where I get dropped off in Oxford)?
The major well-known car hire companies all have their offices on or just off the Botley Road, the main road into Oxford on the western side. They either have their own meet/greet/pickup service from the stations, or refund taxi costs by presentation of a receipt.
When I was in Oxford I used Enterprise...they'll bring a car to you anywhere which is really convenient. You do have to take them back to their office before you go on your way but it's not far at all from the city center. I found it to be very easy and far better than trying to hunt for the office myself.