Big Weapons
Car Engine -- If you completely destroy a car (ex. a bazooka shot), you can grab the car's engine. This only works with Smasher.

Airplane Gun -- On the Air Base stage, go inside the hanger and destroy the plane. After it is destroyed you will be able to use its gun.
Submitted by Randy Kitchens and Corey Cobine

Double Team
In the co-op mode ,when you throw an enemy or boss, the other player can hit the enemy that is being held.
Submitted by EPG

Easy Money
To get more money in the game roll around the walls. Walk up to the wall and start rolling. Make sure you roll against the wall and not just by it. Money should come out. We know this sounds crazy, but it works.
Submitted by Thomas DeGravel

Find Flare Guns
On the hovercraft stage there are two black structures on either side. Destroy those and a flare gun will drop out of each structure.
Submitted by Airboarder10

Floating Character Glitch
Play with two players, when you get to the level 2.2 (Truckdriver) Let the truckdriver pick one of you up, when he's about to throw you down have the other player knock the Truckdriver down. you'll be floating while the other player will not. it's funny but you can't get down unless you restart the game.
Submitted by cyberspook

Level Select and Invincibility
At the main menu, PRESS and HOLD L + Z + C-Up + C-Down. This will take you to the character select screen in a few seconds. From there you may press C-Left or C-Right to choose your starting level. You will start with invincibiliy.
Submitted by Aaron Ramsey

Out of change
When entering the subway in mission 4.1 you are stopped by toll machines. There are two ways to get through them, you can either destroy them or pay the toll. To do this there is a payphone on the wall to your right. Just hit the phone and grab a coin. Then walk to up to one of the toll MACHINE(not the bar) and the bar will pop up and you will be able to walk through
Submitted by Rodger & Shaun (Brisk5)

Rocket Launcher
On the car park stage if you break the police car a rocket launcher will come out the trunk.
Submitted by joe

Special Moves
Each character lists a special move at the end of their character bio. Each of these button configurations work for all charcters giving each chracter 4 special moves.
Submitted by Kevin Underhill

Thirsty?
In some levels(1.2 and 4.1) there are coke machines. If you break them until you cant break them anymore you will find three coke cans witch refill some of your energy and also a metal bar.
Submitted by Rodger & Shaun (Brisk5)

Weapons on the First Stage
As soon as you start the level, there is a police car to your left. Destroy it and a weapon will come out the trunk. After that you go through the gate and you should see a black car. Destroy it and another weapon will come out of the trunk.
Submitted by Tony Chung