How do I determine the VFR pattern altitude at an airport?
In April 2013, the FAA's Charting Group met to discuss this question.  The standard pattern used to be 800 ft AGL, and the Chart Supplement (formerly called Airport/Facility Directory or A/FD) was inconsistent in listing them.  Ultimately they decided: 


  Chris Criswell, AJV-22, reported that, per ACF recommendation, all traffic pattern altitudes, standard and non-standard, will be added into NASR (the AFD) for all airports. This will be a day forward implementation beginning in July 2014. 


Some other places the TPA is recommended to be 1000 feet AGL:

Advisory_Circular AC90-66A 


  c. It is recommended that airplanes observe a 1000 foot above ground
  level (AGL) traffic pattern altitude. Large and turbine powered
  airplanes should enter the traffic pattern at an altitude of 1,500
  feet AGL or 500 feet above the established pattern altitude. A pilot
  may vary the size of the traffic pattern depending on the aircraft's
  performance characteristics.


The Chart Supplement (A/FD) will typically list the Traffic Pattern Altitude (TPA) if it is non-standard (not 1000 ft/1500 ft AGL)

The FAA's Airplane Flying Handbook says


  The traffic pattern altitude is usually 1,000 feet above the elevation of the airport.


Now the Chart Supplement (A/FD) will be the definitive guide!