What US airports have approaches with LAAS?
The Local Area Augmentation System was the FAA term for the Ground Based Augmentation System (GBAS), which is an International Civil Aviation Organization (ICAO) standardized system for local area differential systems. 

The FAA has migrated to the ICAO term GBAS, though Several historical FAA documents still retain the LAAS terminology.  

According to the FAA GBAS FAQ page,


  Currently, two U.S. locations have obtained operational approval for public GBAS use and support revenue airline traffic. These stations are located at Newark Liberty International Airport (EWR) and Houston George Bush Intercontinental Airport (IAH). 


According to FAA, development of GBAS continues and,


  The FAA and other States are in the process of validating proposed ICAO GBAS standards to support Category III (CAT-III) precision approach operations. The FAA expects ICAO will approve GAST-D Standards and Recommended Practices in 2015


Also,


  The FAA continues to validate the GBAS CAT-III requirements as part of the Next Generation Air Transportation System (commonly known as NextGen). The FAA has currently deferred any Federal acquisition decision on GBAS. 


Also, though GBAS and WAAS are mutually exclusive at present, some future aircraft like A350 are expected to support both GBAS and WAAS.