There isn't much to unlock in WWE All-Stars, really. Just all the rest of the wrestlers, for the most part.
But if you want to unlock everything, enter this on the main menu:
"Left,Y,Down,Left,Y,X,Left,X,Y,Down,Right,X,Left,Up,X,Right"
The direction controls are just the basic analog stick directions.
I originally thought this was a stupid lie, and a dumb joke posted on a website, but it's actually true. It really works. Imagine my surprise.