The is the standard window model, and the panel, but what is the model without the side rear windows referred to as?

 

It's referred to as a half panel. Unlike the full panel, it has "normal" type passenger doors, so calling it a half panel could be considered incorrect maybe.
(or maybe not. just my thoughts here )

Some folks also refer to it as the AA5. That comes from the RPO code that shows the car has the rear window delete option.

 

To expand on George's explanation of the AA5 RPO code, the three body styles in GM-ese are.

RPO - AXP Vehicle Type - Multi-Purpose Passenger Vehicle (Wagon/SUV Version)

RPO - AXS Vehicle Type - Panel Van (Panel Version, No Rear Seating Provisions)

RPO - AA5 Window - Rear Quarter-Delete (Wagon/SUV Version With Rear Seating, Blanked Rear Quarters)

We've kind of settled on "Trucklet" as a general nickname for HHR's.

With "Wagon", "Panel", and "Partial Panel" as the accepted terms for the body styles.

 

I like the Trucklet name lol!

The rear quarter window delete, is a nice option for a different look and still allowing passengers windows. I still think the panel is the coolest, even my wife agrees, of coarse it's after I purchase 3 windowed HHR's lol.