I found all the orbs the hard way over the weekend, but actually managed to find this PDF which maps out all the orbs for you. It's pretty cool; it shows you a shot of where you'd be on the map next to a screenshot of the agent looking at the orb on-screen. It's about 20 megs, but is worth it if you haven't found all the orbs yet. I wasn't able to upload it to this forum, but it can be downloaded here: http://putstuff.putfile.com/51812/9958273
EDIT: Though helpful, this map definitely does NOT contain the locations of all the hidden orbs (i just found out the hard way).
same here...i got to 285 hidden orbs, and then broke down and started going through the list. I also just noticed that, while it lists all the supply points and races, it doesn't list the stunt markers. So if there's anybody that wants to search for stunt markers, or do some road races, send me an invite!