In my experience as a driver, here are my top 5 POI databases
for you to download for your GPS. (Free & paid).
Speed cameras
http://www.gps-data-team.com/poi/united ... _Trap.html
Low clearances
http://www.lowclearances.com
Truck stops
http://www.poifriend.com/poigroup.php?poigroup_id=6749
Gas stations
http://www.gps-data-team.com/poi/united_states/petrol/
Walmart
http://www.poifriend.com/poigroup.php?poigroup_id=406
I have all of these installed and they all work really well.
Safe driving.