Area 51 Warp  -  In the multiplayer Area 51 level there is a UFO. If you shoot the UFO you get this cool gyrating light show. In between the upper left and upper right corners is another UFO. If you blow both of them up and drive into the light show you can warp between the two points. 

Better Weapons  -  To get better weapons in multi-player collect 15 or more of a weapon and press A+B at the same time. You will fire a modified blast of the weapon you fire. This code doesn't work with grenades. 

To activate a cheat, highlight “Input Code” at the Options screen and enter the corresponding code below.

All gangs (Campaign mode) LTSLTSGNGS
All weapons PLVRZM
Invincibility MSTSRVV
Invisibility CRSTLCLR
Plague of Frogs FRGZ
Psychedelic view HVRL
Storm Ravens gang WMNRSMRTR
Story mode CDPLT
Toads replace Queen Lords TDZ
Unlimited ammunition LTSFBLLTS
Unlimited lives LVFRVR
Trippy mode CNCTHRTM

Manual Camera  -  In a 2P game with two computers enabled, kill one player quickly. The loser’s portion of the screen should be static, but under the control of the analog stick! 

Mines, Swarmers, and Lasers  -  With MINES as your chosen weapon: Press A+B simultaneously and it will lay down all of your mines behind you. 

With SWARMERS as your chosen weapon: Press A+B simultaneouly and it will fire all your swarmers in rapidsuccession. 

With LASERS as your weapon: Press A+B simultaneously and it will shoot your laser causing a multi ricochet. Note: It will not ricochet off tanks. This cheat appears to work on every level and against every tank. I think you need the ALL WEAPONS code for this to work correctly. (All weapons code: PLVRZM) 

Passwords  -  To play on a particular level, highlight “Input Code” at the Options screen and enter its corresponding password.

Level 01: Ground Zero -- FRHBMCTNTK 
Level 02: The Tunnel -- LHTSPMFRGS 
Level 03: Times Square -- NGLFFPTTFP 
Level 04: Stranglehold Bridge -- SHPPNRVWGB 
Level 05: Bonus Level -- MRFFCRTKP 
Level 06: Heartland -- LPGCVBBJCF 
Level 07: Lake Shore Drive -- GLWHJCRNLK 
Level 08: State Street -- KMKJTMHRNS 
Level 09: Bonus Level -- FLWWFCWNRK 
Level 10: Armageddon Highway -- WSMBCPVRWS 
Level 11: Area 51 -- CGJWVRGLNM 
Level 12: Fremont Street -- KVVLHFHWTB 
Level 13: Bonus Level -- FCLPJRWTMP 
Level 14: Crimson Gate -- TMFNJMKJGF 
Level 15: Warf -- PPJLJHRCVV 
Level 16: Bonus Level -- LNKNSWKGTH 
Level 17: Q-Zone -- WMNRSMRTR 

Place Gun Buddies Behind Walls  -  First start a game on any mode or level. Next pick up a Gun Buddy. Now back into a indistructable wall and try to lay it. If it dosen't work back up more and try again. Once you've laid it turn around and all you can see of it is the two barrels on the front of the gun. Now when a opponent comes by it will shoot it even though it is behind the wall and the enemy can't shoot through the wall so the enemy can't destroy it. 

Self-Destruct  -  To blow up your tank press and hold all four C-buttons. This can be helpful if you want a different tank in Deathmatch. 

Shoot lasers from advanced guided missile  -  When you have more than fifteen guided missiles, select it and press and hold A+B at the same time. If done correctly the missile will be bigger and slower than the normal ones. Then while guiding the advanced missile press Z to fire lasers from the tip. (You only have a limited amount of lasers that can be fired. This does not use the lasers that your tank has.)