The Forge comes up with some nutty stuff, but some of the names have that ring to them - you know they'll be awesome and memorable. Here's my first crack at it. Numbers have been left out so everything's compatible with your favorite system.
TAKER CAT - Obviously, this is a cat that takes your shit. It doesn't sneak up in the middle of the night, though. You find it in the dungeon, scared and alone, about to be eaten by hobgoblins. Your girlfriend's PC picks it up and puts it in her backpack so just its cute widdle head sticks out. THEN, when you're all asleep, it takes the most valuable magic item it can carry, and its observations about the party, and scampers down 2 levels of the dungeon to the arch-wizard who runs the place. It is, of course, his familiar.
Stats for a regular cat, except for high intelligence and charisma (cuddlyness). If the PCs wise up to the trick, they can hold it hostage or perhaps just kill it at a critical time in the battle with the boss wizard... if they can look into those big, cute, cuddly eyes and still swing the sword, that is.
FLESH SERPENT - The hot dog of the undead, this "snake" is made from whatever floor-scrapings and castoffs are nearby. Perfect for an on-the-go necromancer! Gnome intestines? Orc tongues? A few mismatched eyeballs? Elf scrotums? Just throw them together, add some sharp teeth and drop it down the chute on top of those pesky adventurers.
Use the stats for your favorite snake, add the 'zombie template' and then make it slippery, foul-smelling, gooey and gross. Venomous bite is optional, but it should at least have some kind of parasite or disease from all that raw meat in there. Can also provide clues about the creator's (former) allies or favorite foods. Hurl!
NEEDLE APE - Hilarious! Some fucked-up wizard crossed an ape and a cactus in the worst way. An ape with cactus needles in its mouth instead of teeth. Can't eat solid food, and its spike-mouthed existence has made it really pissed off. It bites you and leaves a whole bunch of needles in the wound. Some needle-apes are rumored to have spikes over their whole body, and the bad attitudes of such creatures are the stuff of legend.
Stats for your favorite primate, but with a horrifying cactus bite attack. It can bite 3 times per day, then must wait 24 hours for the needles to grow back. After being bitten, the needles will stay in the wound and deliver a paralytic plant juice. Save vs. poison or lose 1d4 DEX per day until it's cured or you reach 0 and die. Greater Needle Apes are left up to your imagination (hint: they are huge prickly assholes).
CANDLE SALMON - These salmon look normal during the day, but at night they light up inside; imagine a fish that swallowed a few of your Christmas lights. Some nobles keep them in their garden ponds as living night-lights, but there are many other applications for a Candle Salmon. The oils inside their fishy bodies make them extremely flammable. Pull one of these out of the river and set it to the torch, it'll burn up in 2 rounds, leaving nothing but a grease spot. Used carefully, they make a half-decent substitute for flasks of oil. A few mishaps with these have given rise to the phrase "burning the Candle Salmon at both ends."
Stats are for a regular fish, except they can't possibly sneak up on you.
This post brought to you by early Frontline Assembly and Wellington beer.