Golden gun:

To grab the Golden Gun, finish 'Trouble In Paradise' with a 'Gold' ranking.
~To get a 'Gold' ranking: be accurate, shoot for the head, try not to get shot at all, find secrets, and kill enemies by blowing up barrels~

Multi-play Golden Gun:

Finish the Precious Cargo level with a 'Platinum' ranking and every 007 icon.

Golden CH-6:

For the Golden CH-6 (and unlimited explosive firepower), finish the Precious Cargo level with a 'Gold' ranking.

Golden Accuracy:

For some truly wicked auto-aim, finish 'Bad Diplomacy' with a 'Gold' ranking.

Golden Clip:

Finish 'Cold Reception' with a 'Gold' ranking.

Golden Grenade:

Finish 'Night Of The Jackal' with a 'Gold' ranking.

Golden Bullet:

Finish 'Poseidon' with a 'Gold' ranking.

Golden Armor:

Finish 'Forbidden Depths' with a 'Gold' ranking.

Unlimited Golden Gun Ammo:

Finish 'Evil Summit' with a 'Gold' ranking.

Unlimited Car Rockets:

Finish 'Dangerous Pursuit' with a 'Gold' ranking.

Unlock the Rocket Manor Multi-Player Level:

Finish 'Trouble In Paradise' with a 'Platinum' ranking and every 007 icon. This multiplayer level is basically a large, open arena that only allows rockets.

Unlock the Stealth Bond Skin in Multi-Player Mode:

Finish 'Dangerous Pursuit' with a 'Platinum' ranking and all 007 icons.

Unlock the Guard Skin in Multi-Player Mode:

Finish 'Cold Reception' with a 'Platinum' ranking and every 007 icon.

Unlock the Alpine Guard Skin in Multi-Player Mode:

Finish 'Streets Of Bucharest' with a 'Platinum' ranking and every 007 icon.

Unlock the Cyclops Oil Guard Skin in Multi-Player Mode:

Finish 'Poseidon' with a 'Platinum' ranking and every 007 icon.

Unlock the Poseidon Guard Skin in Multi-Player Mode:

Finish 'Mediterranean Crisis' with a 'Platinum' ranking and every 007 icon.

Unlock the Carrier Guard Skin in Multi-Player Mode:

Finish 'Evil Summit' with a 'Platinum' ranking and every 007 icon.

Rapid Fire Power-Up:

Finish 'Fire And Water' with a 'Gold' ranking

Regenerative Armor Power-Up:

Finish 'Mediterranean Crisis' with a 'Gold' ranking.

Unlock the Calypso Gun in Multi-Player Mode:

Finish 'Fire And Water' with a 'Platinum' ranking and every 007 icon.

Unlock the Full Arsenal in Multi-Player mode:

Finish 'Forbidden Depths' with a 'Platinum' ranking and every 007 icon.

Unlock Gravity boots in Multi-Player Mode:

Finish 'Bad Diplomacy' with a 'Platinum' ranking and every 007 icon.

Unlock the Viper gun in Multi-Player Mode:

Finish 'Night Of The Jackal' with a 'Platinum' ranking and every 007 icon.

Lotus Esprit car:

Finish 'Streets Of Bucharest' level with a 'Gold' ranking.