There are 18 vehicle jumps in RAGE, you'll get the Jumper achievement for completing them all. You can see where they are by the floating things.
Beginner's Jump - Right outside the ark, headed towards Wellspring, there is a mound in the middle of the road. Launch off it into the floating thing.
Butterfly in the Sky - Right near the Beginner's Jump. Actually start on the Beginner's Jump and use the slant to get it.
Tiger Jump - Coming from Wellspring, take a left and head under the highway, you'll see it floating above some rocks to the right.
Mini Gap Jump - Coming from Wellspring head right and stay to the right until you see a jump on the left. Take it and nail the floating thing.
I Think I Can - Coming from Wellspring head to the right, but stay to the left and launch off the ramp to an upper area.
Leap of Faith - As you enter the Scorcher Territory, there is a piece of highway that points straight up, boost off of it.
Highway Hop - As you enter Scorcher Territory, take the on-ramp to the left. Head up it, then turn around stay to the left and launch off the end of it into the floating thing.
Dedicated - Next to the highway at the Northern Tower.
Science Makes You Crazy - Past the Northern Tower above Kvasir's Chasm
Crazy - To the left right as you drive up to Crazy Joe's.
In the Basket - Just north of the gate to Hagar's Territory. It launches you into a crater.
In the Gears - Just to the left of the Power Plant off a ramp.
Shock and Awe - Above the Power Plant, climb up the cliffs to launch off.
Gimme - Straight outside Subway Town, you have to hit this one with a lot of speed to reach it.
Bunny Hop - Take a left leaving Subway Town and it looks like there is a jump to your left to get it, but you actually need to drive past the jump, go up the on-ramp and stay to the left to hit it from above.
Over the Hill - Take the same on-ramp as you did for Bunny Hop except stay right and you'll see a jump made out of street signs to your left.
Off the Dune - Past the Authority Bridge, go through the arch on the right and launch off the dune to the left.
Near the Heart - Past Off the Dune there is a tank spawning building to the left, drive to the left of it and launch off the cliff behind it.