Greeting cards remind us of so many things, like that people actually do care about us, that good poetry is tough to write, and that even grave illnesses are considerably funnier when they involve a monkey on a tricycle. For cards that will remind you of nothing you've ever seen before, pick up some Mechanicards
Mechanicards are just about the craziest thing since that taxi game, called Crazy Taxi: a series of cards made of paperboard and bits of wood, metal, and plastic which arrive flatpacked and unfold into tiny yet intricate paper machines that do all sorts of cool stuff, and serve as "visual and literary metaphors for human social interaction", which you'll eventually have none of if you keep sending those Blue Mountain cards. Some of the mailers
The Radial Engine The first one out, this card features a drawn-like-a-blueprint, 7-piston, actually "working" radial engine (think old prop airplanes) that's crank-powered, just like that dude running around the trailer nonstop at 4am
The Ambigulator With damn-near-Seussical illustrations, and employing workings similar to an old train's drive wheels, this assembly answers questions by sliding an optical filter up and down, producing answers of "Yes" and "No", making it twice as effective as asking the Prog Rock section of FYE
The Yike-a-cycle Featuring a unicycle with a pair of robot legs and a copper-colored track, cranking the gearing on this sucker gets legs to power a unicycle endlessly around the circular track, making it kinda like NASCAR, only not the worst
You can pick up a subscription that gets you all five cards, and you can also buy them individually as they're launched, although since they're super-limited, there's no guarantee you'll get them all with that kind of monkeying around.