I have some plans on making a bunch of custom targets to practice on, since ones I want don't seem to exist and silhouette and bullseye targets get old after a while. After my ponderings on Choose Your Weapon I decided that I definitely want some space bugs monster horde targets (Zerg, Tyranid, whatever the things were in Starship Troopers, maybe the Flood ala Halo).
A friend suggested the Necromorphs from the Dead Space series (an interesting challenge, you HAVE to shoot for the limbs for bullets to be effective on mutant space zombies).
Dinosaurs, (mutated, cloned, space, or otherwise) seem like they could be fun. Do some research, have some set up as "charging treat" targets, have others modeled after hunting practice targets with the score zones over critical locations.
EDIT: Kate suggested Terminators/robots. I wholeheartedly agree, and there don't seem to be any readily available for purchase or download. This'll definitely be one where I need to offer them as hunting targets with highlighted weak spots.
I know there are at least one or two people who swing by to glance at my ramblings because the counter keeps ticking up, so if you have any thoughts on interesting baddies you'd like to put a few rounds through, speak up! I'll be drawing some of these up next year when I have time, since nobody offers good targets for sale. I can at least make free "print your own" targets available, if not get big ones printed out on better paper.