Greebly, greeble, or nurny - which is correct? I don't know - I first ran into the term in the infamous Star Wars Sketchbook by Joe Johnston, on the Millennium Falcon pages. A note for the set designers that something called a "mechanical greebly" will hang down from the underside and help hide the set.
That's a pretty large-scale one though - most of the greeblies model-makers concern ourselves with are little bits and bobs that we can use to imply detail or complexity, catch the eye, or simply break up large blank surfaces. Most model makers with any eye toward scratch building have a few piles of unused parts, sprues, etc., to use for greeblies. Or a few bags.
Drawers.
Bins...
We can quit anytime we want.
One of my "standard" greeblies is the good old "googly eye":
These kinds are of an "ultra-low-profile dome roof" shape. (I looked it up.) They come in various sizes so they're pretty useful.
Side views included with cat hair:
I use them for hull bulges on spaceships, end caps for cylindrical forms, and the like. Sometime I cut the bottom stiff paper off and remove the loose eye disk for yet another type of greebly. Most recently I used them to build and cap the fuel tanks for my cardboard semi truck. I highly recommend having a bag or two around.
