Real names
When creating a wrestler, you can make people such as Ric Flair, Hall, Nash and others and the announcer will actually say their names.

All wrestlers
At the main menu, press Up(2), Down(2), Left, Right, Left, Right, Triangle(2), Square to unlock all wrestlers.

Increase Smackdown Meter
Press the taunt button rapidly during a match (this will leave you open to attack). Your meter will fill to its full level.

Get Dory Funk
Beat career mode using Tony Funk

Get Jimmy Hart
Beat career mode using a Loved wrestler

Get King Kong Bundy
Use career mode to finish the Southeast territory

Get Robert Gibson
Beat tag tournament

Get Ricky Morton
Beat tag tournament

Get the Erichs
Beat career mode with Kevin Von Erich

Captain Lou Albano
Finish career mode with a wrestler in the "Hated" category.

Ivan Koloff
Win the versus tournament.

Mr. Fuji
Win the Tag Belts in tournament mode.

Sabu
Finish career mode as The Sheik.