freewill  -double speed in single player mode.   
Gulliver  -the Porsches are all shrunk down to the size of radio controlled racers and have little antennas. 
Smash Up  -using the Skidpad, Destruction Derby style racing.
Dakar     -tired of Street Racing? Changes car physics and tracks to Rally style. 
Fuzzyfuz  -enables cops in quick race (cops may not appear on all tracks: i.e.-Monaco). 
yraGyraG  -enables all cars to have 993 physics. 
fetherw8  -this cheat code makes cars way heavier.

All Cars and All Tracks:
Go to the multiplayer option and choose Peer to Peer. Now you can race with all cars and on all the tracks. It isn't neccesary to play with others...you can do it alone.

Infinite Money on Evolution Mode:
Buy a used car and do an OVERALL repair. After repairing, the value of the car will be higher than the price that you payed for it, and the repairs. Sell the car and notice that your money will be higher than your initial one. There is an infinite number of used cars in the shop so, just do this infinite times to have infinite money.

Thanks to Revolution reader vincent osinga, Travis Soverns and Guilherme Prista Esteves!