The head of Alfredo Garcia.

This is a no brainer. El Jefe offered a million bucks for this scoundrel's head. You can buy it on eBay for $1,500, HERE.
The head's description reads:

This Head was designed by the infamous  John Chambers, who designed  Planet Of The Apes,  and many more. I'm Nico De Silva, the actor, in the  picture title, Bring Me The Head Of Alfredo Garcia.. John Chambers made three others. This is the original and only one  I know available.  Its a collectors "must have" item.  Sam Peckinpah  also directed Classics such as;   The  Wild Bunch-Pat Garrett & Billy the Kid-The Gateway, and more more.

 This would be an amazing collectible to have on the shelf.