When you complete the following tasks the corresponding costume will become an available option.

Unlock Cosmic Spider-Man:
Complete Act 1.

Unlock Armour Spider-Man (Black and Greys):
Complete Act 2

Unlock Ben Reily:
Complete 25 City events.

Unlock Spider-Man 2099:
Complete 50 City events.

Unlock Iron Spider-Man:
Collect 150 Spider Tokens

Unlock Spider-Carnage:
Defeat 500 enemies

Complete the indicated task if you want to get an assist from the following characters.

Big Wheel:
After beating Tinkerer keep selecting the 'bad' choice when asked by computer.

Black Cat:
Select to save Black Cat when you fight her (pick the 1st choice when asked by Smythe)

Hobgoblin:
Before fighting Kraven keep selecting the 'bad' choice (the 2nd/3rd choice).

Jessica Drew:
Before you fight with Jessica Drew Select to help S.H.I.E.L.D crew from the symbiote.

Luke Cage:
Select the 'bad' choice (2nd choice) when you asked by a man who says he can divert the train containing symbiote.

Shocker:
Choose to free Shocker when you have defeated him.

Solidarity:
When you have defeated Shocker take him to jail.

Storm:
When you have defeated Tinkerer keep selecting the 'good' answer when asked by computer.

Random Assist:
When you beat any level or buy the ultra rare power ups you will be able to get a random assist from the following characters - Mysterio, Night Crawler, Wolverine, Galactus, Hypno Hustler Ctylok.

When Wolverine attacks you he will ask a series of questions that must be answered correctly, below are the answers to that quiz

Question 1:
Answer: Richard and Mary

Question 2:
Answer: Ned Leeds

Question 3:
Answer: Battleworld

Question 4:
Answer: Daredevil

Question 5:
Answer: A Mutant

Question 6:
Answer: May Parker

When you have beaten the game enter the following codes at the cheat menu to unlock the corresponding characters.

Unlock Moon Knight:
Enter the code CRESTWARRIOR

Unlock Rhino:
Enter the code MASSIVEHORN

Unlock Venom:
Enter the code IEATYOURBRAINS

When you have collected 1,000 spider tokens, ALL the spider tokens will appear as red dots on your mini map.

After completing the game view the credits until they end and the game will return to the 'Title' screen. Select 'Continue' and the game will run through the credits a second time (don't skip them) and once again return you to the 'Title' screen. If you now select 'Continue' when prompted you will begin a new game starting at the first cut scene and you will have retained ALL the upgrades and collectables you had from the previous game.