If its top dollar, then you can't go wrong with the Randolph, scene of many morse films and the place that people like the Sultan of Brunei and other such's stay.
A bit cheaper, you have the Old Parsonage which is a gorgeous little place just north or the town centre, or there is Mal Maison, right in the centre, and built into the old jail house, really nice rooms and a great atmosphere.
If you want the real oxford experience, contact the colleges, during the summer they have loads of free room available, are extremely central, pretty cheap, and you get to say that you stayed in an oxford college. I can recommend some if you don't want to get in a duff one.
The old bank hotel is pretty darn nice, and I've heard that the cotswalds lodge is nice as well. There is also the four pillar/oxford spires hotel.
If you aren't bothered about staying actually in Oxford, then you can save a bit of money by staying at either the Holiday Inn Oxford, or "The oxford hotel" which are both located to the north of the city, right next to the park and ride so you can get to and from oxford really easily and relatively cheaply, and the ride only takes about 10-15 mins depending on traffic, and runs till about 11pm if you are having dinner.
I lived there for 3 1/2 years, so if you need to ask anything, just drop me a line on here and I'll do my best to help.
