Carrion crawler is a dungeon-dwelling scavenger that sometimes hunts living creatures, paralyzing them with its tentacles and devouring them. I don't remember if I have ever used these creatures in D&D, but they look very fitting for a generic dungeon monster. Very weak to ranged attacks and high HT characters.
Bulette is a fun and memorable monster from D&D Monster Manual. The bulette, or landshark, tunnels underground and then ambushes its prey, pouncing on it and grabbing it with its powerful jaws. Uneven DR makes the head and top hard to penetrate, but leaves limbs and belly more vulnerable.
Bodaks are the undead remnants of humanoids who have been destroyed by the touch of absolute evil. I have never seen them as very appealing monsters, but I think a Dragon Magazine article makes them more interesting.
Blink dogs are intelligent canines with a limited teleportation abilities. Blink dog is an iconic D&D monster that I have used occasionally, but never in GURPS. At least yet.