Great post fop.
Will Ferrell is the toughhest signature in Hollywood. Not impossible, but tough. And he can be a real jerk- like, berating to you. I'm sure he has signed his share and in fact he used to be pretty good. But he's been ranked the worst one by autograph Magazine for five or six years running. I've heard it from too many people....
Eminem many be tough in person but his Bravado website normally has signed lithographs there. I have one of those. For $250, it's a pretty good investment.
The Floyd guys are tough- they are well aware of their value.
Some of my better ones:
Mick Jagger times four along with one Stones piece
Madonna times six or seven...
REM complete with Bill Berry
My wish list is pretty much Bob Dylan.