It's really a hard one to nail down but here's the one's that jump to mind immediately:
Ugly Ducklings - "Nothin". It's a very weird press on Arc records out of Toronto who I believe were the parent company of Yorkville (the press you normally see). Also, the b-side is their other big hit "Gaslight". Nobody I ask seems to know anything about it. I paid 4 bucks for it about 12 years ago.
Trashmen - "Surfin' Bird". It's not that crazy or rare, but it's an Aussie press I bought for less than a buck at a bookstore when I was down under. I also got Oz presses of Blue Cheer - "Summertime Blues" and Troggs - "I Can't Control Myself" and Jumpin' Gene Simmons - "Haunted House" for the same price at the same place. All killer records if not super rare.
Shadows of Knight - "Shake" pic sleeve. Found at the bottom of a box full of real shitty 80s jukebox 45s.
49th Parallel - "She Says" I just really dig the B-side "Citizen Freak".