Cruis'n USA                 

Extra Vehicles: To drive the Autobus,Jeep or Police Car, hold one of the
"View" buttons and press Start while choosing a vehicle. This trick works
in the arcade as well. 

Race Segments: At the Race Selection screen, hold the appropriate buttons
to access the different levels. 

* Indiana Segment - hold L, (right) C, (upper) C
* Golden Gate Bridge Segment - hold L, (left) C, (lower) C             
* San Francisco Segment - hold L, (right) C, (lower) C

Easy Upgrades (two player mode): Start a two player game and race until 
you reach Washington DC.  When the DC race begins, press start and quit 
the game.  Next have player #1 return to Washington Dc and upgrade his 
car.  After player #1 has finished player #2 should do the same.

Flashing lights and siren:  Race as either the Bs or the Fuzz.  While 
playing tap Brake, Brake and Gas to flash your lights or siren.