Enter the following at the Cheats menu:

Stiffcomp       Unlock everything

Neverboard      Unlock all boards for selected skater

Juice4me        Max stats

Rollitall       FMV sequences 

WeEatDirt       All created skaters 

Unlock Neversoft team Members:
Enter the following as Created Skater Names...

Aaron Skillman (also by entering Aaron, Skillman, or ARS)

Alan Flores

Andrew Rausch (also by entering Jujy)

Andy Nelson

Brian Jennings (also by entering BDJ or Brian)

Captain Jennings (also by entering Cap'n Jennings or Capn Jennings)

Chad Findley (also by entering Stallion or Doofus)

Chris Glenn

Chris Rausch (also by entering Team Chicken, CJR, or Rausch)

Chris Ward

Connor Jewett

Darren Thorne (also by entering Darren or Thorne)

Dave Cowling

Dave Stohl

Edwin Fong (also by entering Maya's Daddy)

Gary Jesdanun (also by entering Garvin or Garvin Jesdanun)

Henry Ji

James Rausch (also by entering My Jamie)

Jason Uyeda

Jeremy Anderson

Joel Jewett

Johnny Ow

Junki Saita (also by entering Kage)

Kevin Mulhall (also by entering Guilt Ladle)

Lisa Davies

Mark Scott (also by entering Hi Ben)

Matthew Day

Mick West

Mike Ward

Nicole Willick

Noel Hines (also by entering Noel or Hines)

Nolan Nelson

Paul Robinson

Pete Day

Rachael Day

Ralph D'Amato

Ryan McMahon

Sandy Jewett

Scott Pease (or by entering Scott Pease, Spease, or Cheesy Peasey)

Steve Ganem

Steven Rausch (or by entering Wevenowski)

Trey Smith

William Pease (or by entering Wild Bill) 

Unlock X-ray skater:
Beat all 54 goals and get gold on all the competitions with 2 different skaters.

Unlock Wolverine:
Beat all 54 goals and get gold on all the competitions with 4 different skaters.

Thanks to Revolution readers crazy_skater, michael, Nick, sunny, Jacob Buckles, Slacker, Laurent, Mardy J. Superfly, M D, and Ben Jenkins!