Arizona

Grand Canyon
Here's talk of an LRT being put, in all places, at the Grand Canyon.
Announced December, 1998: the 14 km LRT for the Grand Canyon has been approved.

Phoenix
LRT (planning stages)
Valley Connections - A 32.6 km proposed system is awaiting funding approval from the federal government.
Airport light rail route explored

Tuscon
Proposed LRT
 
Old Pueblo Trolley
A Proposal For an LRT stop in Tuscon