Big heads:
Select the "New Season" option at the main menu, then press L1, R1, L1, R1, Circle, Square.

Super player:
Enter the settings screen and select "Rosters". Create a player and copy Kobe Bryant. Change his statistics to 6'9", 225 lbs., and rename him Kenyon Martin. This player can make any reasonable shoot.

Dunk contest moves:

One-handed Dunk: Press Left, Right during your run up, then press X.
Back Jump: Quickly press Up, Left, Down during your run up, then press X.
Back Change: Press Left, Right during your run up then press X.
Power Dunk: Press Up(2) during your jump.
Clutch Dunk: Press Down ,Up during your jump.
360 Slam Dunk: Quickly press Up, Left, Down, Right, Up during your run up then press X.

Special moves:

Back Change and One handed Slam
Press Left, Forward, during your run up then press X. Press L or R during the jump at about the freethrow line.

Back Jump and Clutch Dunk:
Quickly press Up, Left, Down during your run up, then press X. Press Down, Up while in the air.