Unlock EBGames bonus level:
Select the "Settings" option at the main menu, then select the "Cheat Codes" option. Press White, Y, X, Black to unlock the EB Games multi-player level.

Weapon Upgrades:

Healing Tool
Fast Injector - Faster doses mean faster health restore.
Health Boost - Adds one life point.
Adrenal Boost - Adds one more life point.

Bulldog
Fire Accelerator - Increases fire rate.
Recoil Stabiliser - Increases accuracy.
Armor-piercing - Increases damage.

Grenade Launcher
Remote Detonator - Increases ammo to 8; allows for manual trigger.
Fragment Attraction - Increases blast size and ammo to 10.
Target Leech - Increases ammo to 12.

Frag Rifle
Servo-Reloader - Increase reload speed.
Magneto Concentrator - Creates a laser mine at close range.
Titanium Concentrators - Creates a stronger mine at close range.

Sniper Rifle
Enhanced Vision - Highlights enemies in scope view.
Increased Ammunition - Increases ammo to 6 in magazine, 18 reserve.
Armor-piercing - Increases damage.

Plasma Gun
Arc Sphere - Charge weapon to unleash damage orb.
Defense Sphere - Damage orb endures longer and explodes on contact.
Explosive Sphere - Damage orb endures longest; explosion is larger.

Rocket Launcher
Heat-Seeking - Warhead heat-seeks after holding trigger and firing.
Dual Warheads - Two warheads fired.
Quad Warheads - Four warheads fired.