While searching for alternatives to the Parallax Ultrasonic Range Finder, I found these 2:

Seeedstudio's Ultra Sonic range measurement module (SEN136B5B) This one is similar to the Parallax one, in that the trigger & pulse width out are on the same pin. See the Wiki Datasheet for specs.

Serial Ultrasonic Motion Detector Sensor Module - Sure Electronics - eBay This one gives the distance via TTL serial. Could this one possibly ease some workload in the EZ-B firmware?