1. Oozes : I like how they can come from anywhere and have different weaknesses and attacks. It's a scary monster like the blob is scary.
  2. Mind flayers : cthulu-esque, psionic cephalovores with paralyzing mouth tentacles.
  3. Kobolds : great low level threat, swarmy and trappy. Fascination with dragons a plus.
  4. Goblins : the world's punching bag, but really they're asking for it. Mischievous, irritating, and in large enough numbers, dangerous.
  5. Beholders : floating eyes with a mouth and even more eyes, rays of death and danger, xenophobic aliens, built-in anti magic death bombs.
  6. Gelatinous cubes : invisible, cube shaped ooze, they make great traps as well as wandering monsters.
  7. Nightgaunts : creepy and silent, they have no faces, melt in shadows, and they can fly.