This forum thread is a constantly updated list of what users of the Game Maker engine have voted to be the best and most memorable Game Maker games ever made. Currently the top ones are:

Seiklus - tapeworm
Jumper (s) - YoMamasMama
Hover Tank 3D - FredFredrickson
Jetz Rampage (s) - Shawn64
Ark 22 - Srehpog

Soldexus - Pneophen
Hard Hat (s) - Damaged
The Jeluvian Project - Pondwater
Ore No Ryomi (s) - Mr.Chubigans
Battleships Forever - th15
Raging Skies - darthlupi