The best guide that I found to grab all of these is here:http://burnout.wikia.com/wiki/Billboards#Billboard_Location_...
Click "show" to reveal the whole walkthrough.
There are picture of each billboard, a point-to-point walkthrough of how to get from one to the next, and video of how to crash through each individual billboard.
I also took their listed recommendation of the Hunter Manhattan (specifically, the upgraded Hunter Manhattan Custom that you receive after completing the Manhattan's burning route), and that worked very well for me. Some of the billboards were actually easier for me with the Manhattan Custom than they were with cars with better stats.