How can I get the 'Trying Anything Once' achievement in Just Cause 2?
Solution 1:
You can find a comprehensive list on the Just Cause 2 wikia with hints on where to find them...
Solution 2:
The Just Cause wiki, now has a list of vehicles and their locations now.
In the menu of the game, there is a Database option and under there is a Vehicle listing which marks which ones you've driven.