Here's one I did:
From Boat to Plane
Basically it's a 20 mile figure 8 Point-to-Point around San Andreas, beginning in the docks, and ending at the airport. Travels fairly smooth, and the checkpoints are rather forgiving (like in one stretch down Raton Canyon, if you fall off the road above on to the one below, the next checkpoint isn't until the two roads meet up). And as I like to tell people, when in doubt, just follow the road.
The only real downside to it is that it takes 15-20 minutes to complete!