Most of the more recent Garmin portable GPS units include a terrain advisory feature. This includes the aera series of portable GPS from Garmin (aera 500, 510, 550, 560).
 

The terrain is generated and derived from a database and GPS reference only. It does not interface with any other external altitude reference sensors. The terrain advisory feature provides TAWS-like color patterns and pop-up alerts when ground proximity or an obstruction lies ahead. The Terrain page provides both overhead and vertical profile views of the topography as well. It should be noted that since the terrain is included on a portable device, it is not to be considered a certified TAWS system by any means.