Sorry for the giant picture; the quality of the scan didn't exactly come out very well. They have the same color scheme as the normal Regis... since I wasn't able to color them, either... Because they were originally intended to be WIPs (not much time for that now, unfortunately), all except Registeel were drawn really
To explain my logic behind each, let's start counterclockwise, beginning with Regice:
Regice: This was partly inspired by the Ice Titan from Disney's Hercules, or more "generic" themes of icicles, plus a bit of the Maplestory Golems (which is one of the types I ran upon while researching golems).
Regirock: The most traditional-looking of the golems in my entry; I would say it's inspired by a "rock gorilla." Those small spikes are supposed to be its legs (but they're farther away from the point of view).
Registeel: A type of metal "dragon golem," Registeel takes parts from normal mechanical or electrical objects, such as a transformer (and Tesla Coil). The poor-looking claws are inspired by bent copper wires.