Costumes...
	Various Steam Achievements...

Basically you have to do side quest's to unlock certain costumes to use the list is below.

Costume	How to unlock
Classic Black Suit	Progress halfway through the campaign.
Future Foundation Suit	Complete all crimes and green side missions.
Negative Zone Suit	Complete all xtreme challenges.
Scarlet Spider	Collect all 700 comics.

Achievement	How to unlock
A Dash of Spider	Complete all XTreme Race challenges
All Tied Up	Defeat 100 enemies by performing Stealth Takedowns
Amazing Spider-Man	Unlock all concept art
Apparent Defeat	Rescue the civilian in the train docking station
Beating the Odds	Clear the second fight against the Hunter robots
Big Apple, Big Worm	Defeat the S-02
Call Interrupted	Destroy a Seeker before it can call a Hunter
Car Hopper	Clear all car chases
Clean Victory	Defeat a Hunter without using your Web-Shooters
Corporate	Collect all Oscorp Manuals
Deeply Sorry	Defeat Nattie
Down for the Count	Win the showdown in the water treatment facility
Friendly Neighbor	Save all hostages caught in petty crimes
FYI I'm Spider-Man	Perform 25 Signature Moves
Gladiator	Complete all Oscorp Secret Research Labs
Haymaker	Perform a Web-Rush punch
Heavyweight Champion	Defeat 1000 enemies
I'm on a Roll!	Achieve a combo streak of 42
Jinxed	Capture the cat burglar
Journalist	Collect all Audio Evidence
Keep It Together	Immobilize 6 enemies simultaneously with web
Librarian	Collect all Magazines
Lightweight Champion	Defeat 100 enemies
Middleweight Champion	Defeat 500 enemies
Negotiator	Resolve all police deadlocks
On the Fly	Collect all 700 Spider-Man Comic Pages
Peace of Mind	Return all escapees to the police
Pest Control	Defeat Scorpion in the city
Peter Parker	Complete the game on human difficulty
Sanitized	Rescue all infected civilians
Siege Averted	Defeat the S-01
Smell You Later	Defeat Vermin
Spectacular Spider-Man	Chain 10 Web-Rushes in the city
Speed Bump Ahead	Defeat Rhino in the city
Spider-Man	Complete the game on super hero difficulty
Stick to the Plan	Defeat 50 enemies by performing Stealth Takedowns
Switched Off	Rescue Alistaire Smythe
Tail? You Lose	Defeat Scorpion in Oscorp tower
Tech Savvy	Collect all hidden Tech Pieces
The Camera Loves You	Complete all XTreme Video challenges
The Sky Is the Limit	Defeat the S-01 without touching the ground
Tomorrow Is Saved	Defeat the S-03
Ultimate Spider-Man	Acquire all upgrades
Vigilante	Complete the game on hero difficulty
Welcome Back, Friend	Defeat Lizard
Who's the Prey?	Clear the first fight against the Hunter robots