All Weapons from Brandon
To get all weapons press start during the game and press z,x,x,z,y,z,y,x, and y. Then you should have all weapons, keys, and items.

God Mode from Brandon
Press start during the game and press x,z,z,x,y,x,y,z, and y. That will give your guy unlimited health.

Level select from Brandon
At Main options screen press x,y,z,z,y,x,y,z, and y. If right you will see level select in blue words at bottom of the screen.