Two hotels close to the University of Michigan central campus area have blocks of rooms available for this conference. Rooms can be booked from these blocks by specifying that you are attending the "US ATLAS Workshop Physics" conference. These two are:
The Bell Tower Hotel at www.belltowerhotel.com . Rooms are guaranteed available if reserved by April 26 at a base rate of $149 per night.
The Campus Inn at www.campusinn.com at a rate of $147 per night single occupancy, $170 per night double.
This same block of rooms is also being held for the US ATLAS Muon Software Meeting being held the following two days at the University of Michigan on May 29/30. See indico.cern.ch/conferenceDisplay.py for more information.
A complete list of hotels in the area is available from www.umich.edu/~info/pdf/accomodations.pdf