These are the unlockable cars and paint jobs.
Unlockable How to Unlock
Carbon Hydros Custom Beat all Showtime Road Rules
Carbon Ikusa GT Beat all Time Road Rules
Carson Carbon GT Concept Find All 400 Smashes
Carson Fastback Get a B Class License
Carson GT Concept Get a Burnout Driving License
Gold Paint Finish Win all Elite License Events
Hunter Mesquite Get a D Class License
Jansen Carbon X12 Land All 50 Superjumps
Montgomery Carbon Hawker Hit All 120 Billboards
Nakamura SI-7 Get a C Class License
Platinum Paint Finish 101% Completion (All Events Completed; All Roads Ruled; All Discoveries, Car Parks and Drive-Thrus Found; Two sets of Online Challenges Completed)
Rossolini Tempesta Get an A Class License
Krieger Carbon Uberschall 8 Complete 2 Sets of Online Challenges
License Upgrades

These are the number of events for each license upgrade.
Unlockable How to Unlock
A License Win 26 events
B License Win 16 events
Burnout Elite License Beat all Events
Burnout Paradise License Win 45 events
D License Win 2 events
C License Win 7 events