GamerMade.com has compiled a guide revealing all unlockable cars that are gifted to the player.
As you finish races in Forza Motorsport 3's career mode, you will receive experience points in the form of XP. As you get to predetermined point totals, you are advanced to the next "driver level." Upon each advancement, you are rewarded with a free car from one of the various manufacturers.
This guide will help players decide better on how to spend their money so that they do not purchase a 2 million dollar car and then unlock it the next race.
BEWARE OF SPOILERS: If you want the level rewards to be a surprise then turn back.