If budget is a concern, we had a very nice stay at the Homewood Suites on the Riverwalk. If you have money to spend, I recommend La Mansion. Hotels dot com has them at $269 per night. The Menger Hotel has good reviews too. A buddy of mine also enjoyed his stay at the Emily Morgan Hotel.
I stayed at the La Mansion a few years ago, and I was very pleased. Very nice accomodations, and the staff was great.