Enter these at the main menu: 


 Unlock Rocky:
 Triangle, Left, R2, Circle, Circle, Select 
                             
 Unlock Pepe Le Pew:
 Left, Right, R1, Circle, Square, Select 

 Unlock Yosemite Sam:
 Left, Right, R2, Square, Circle, Select 

 Unlock Foghorn Leghorn:
 Right, Right, L2, Square, Square, Select 
                             
 Unlock Sylvester:
 Left, Left, L1, Triangle, Circle, Select 

 Unlock Granny:
 Circle, Triangle, Triangle, L1, R1, Select 

 Unlock Duck Dodgers:
 L2, Square, Square, Triangle, Circle, Select 
                             
 Unlock Gossamer:
 Triangle, Circle, R2, R1, Square, Select 

 Unlock Genie:
 Square, L1, R1, Triangle, Circle, Select 

 Unlock Hector:
 Triangle, L2, L1, Triangle, Square, Select 

 Unlock Evil Scientist:
 Square, Circle, L2, R2, Triangle, Select 

 Unlock Duck Dodgers Speedway:
 Circle, Left, Square, Square, R2, Select

 Unlock ACME Factory:
 L2, R1, R2, Triangle, Circle, Select 

 Unlock Planet X Speedway:
 R1, Square, Circle, L2, Triangle, Select 
                             
 Unlock Wackyland:
 L1, Circle, Square, R2, Triangle, Select 

 Unlock Planet Y:
 Right, Left, Triangle, L2, L1, Select 

 Unlock Forest Speedway:
 Triangle, R2, Left, Triangle, L1, Select 
                             
 Unlock Garden Speedway:
 R1, Right, Left, L1, Square, Select