Driving to Salzburg in Sept 2011.
Where have you stayed that you really liked?
Blobergerhof off Moostrasse. Its in RS.
Haus Reichl on Moostrasse is wonderful. You do have to take a bus to the old city, but it is easy to do. (they also have bikes if you want to ride)
Pension Bergland is also wonderful. It is more expensive, but you can walk to the old town. Sadly, since the dollar dropped, it is no longer in my budget range.
We've stayed at the Star Inn Salzburg Zentrum. Just a 5 min walk through the tunnel into town. The bus also stops right in front of the hotel. Basic hotel, good location.
I've stayed at Institute San Sebastian a couple of times. Once as a single in a dorm room and once with wife and three kids in tow. It's very well run, clean and quiet and convenient to downtown. They also let me park my car for free last time I stayed. If you are okay with hostel/college dorm style accomodations, it's a good choice.