Ratchet & Clank: Going Commando:
Challenge Mode and Secrets:
After completing the game, Challenge mode and other features will be unlocked. 

Challenge Mode - Beat the game once
Mega Weapons - Buy from vendors in challenge mode, after getting a weapon's second form
Secrets Menu 1 - Play challenge mode
Secrets Menu 2 - Play challenge mode, get all weapons second form and mods except for Clank Zapper, Gagetron Weapons, R.Y.N.O II or Zodiac. 

Unlock Paint Jobs:
Get skill points and visit Slim's. 

Clowner - 25 skill points
Dark Nebula - 15 skill points
Insomniac Special - 29 skill points
Lunar Eclipse - 25 skill points
Neutron Star - 19 skill points
Paint Jobs - 3 skill points
Plaidtastic - 29 skill points
Prepster - 29 skill points
Scoop Nose - 18 skill points
Silent Strike - 15 skill points
Solar Wind - 15 skill points
Space storm - 10 skill points
Split Nose - 29 skill points
Star Traveler - 19 skill points
Super Paint Jobs - 10 skill points
Supernova - 10 skill points
Warp Streak - 10 skill points 

Skill Point Cheats:
Beach Boy - Get 30 Skill Points
Big Head Clank - Get 10 Skill Points
Big Head Ratchet - Earn 5 skill points
Clown Suit - Get 20 Skill Points
Enemies Have Big Heads - Get 25 Skill Points
Mirrored Levels - Get 12 Skill Points
NPCs Have Big Heads - Get 15 Skill Points
Ratchet in a Tux Skin - Earn 7 skill points 

Unlock Snow Skin:
Beat all 60 levels of the "Impossible Challenge" in the Arena in the Megacorp Games. 

Unlock 'Making Of' Video: Collect 29 skill points.

Rest of Secrets Menu 
See above, get all weapons second form+mods. Does not 
apply to Clank Zapper, Gagetron Weapons, R.Y.N.O II or Zodiac. These can have their first forms. 

Ultra Weapons: 
Upgrade from Mega Weapons. 

Get skill points and visit Slim's.
Clowner - 25 skill points 
Dark Nebula - 15 skill points 
Insomniac Special -29 skill points 
Lunar Eclipse - 25 skill points 
Neutron Star - 19 skill points 
Paint Jobs - 3 skill points 
Plaidtastic - 29 skill points 
Prepster - 29 skill points 
Scoop Nose - 18 skill points 
Silent Strike - 15 skill points 
Solar Wind - 15 skill points 
Space storm - 10 skill points 
Split Nose - 29 skill points 
Star Traveler - 19 skill points 
Super Paint Jobs - 10 skill points 
Supernova - 10 skill points 
Warp Streak - 10 skill points 

Clank's Day at Insomniac: 
Get all weapons, mods, and upgrades. 

Endorsement Deals: 
Get all weapons, mods, and upgrades. 

Paintings: 
Unlock the Random Stuff Menu. 

Random Stuff Menu: 
Enter Challenge Mode. 

Sheep Blasters: 
Get all skill points. 

Space Invaders: 
Unlock the Random Stuff Menu.