Two Good Sources for Random Monsters

Below are a couple collections of links to the monster randomizers written by two prolific designers.

The links in the first collection are by Lum from Built By Gods Forgotten, who used a "remix" approach to randomize the abilities of the most classic D&D monsters.

The randomizers in the second collection are by Richard LeBlanc of Save vs Dragon. He uses a series of d30 rolls to randomize a creature's appearance, combat statistics, and special abilities.

Fortunately, both authors are from the pre Google Plus era of the Old School Renaissance, so they've both made each randomizer available as a one-page pdf. (Richard also wrote a number of unique new monsters, and both wrote a number of other generators worth looking at.)

Remixes - Built By Gods Forgotten

Dragons & Chimera
Esoteric Animals
Fey Woodland Beasts
Fey Woodland Humanoids
Gorgons Lycanthropes & Gargoyles
Humans
Humanoids
Otherworldly Monsters
Slimes Molds & Jellies
Undead

BONUS - Treasure Maps
BONUS - Treasure Hordes

EXAMPLE - The Widow of Hamelin is a beautiful woman's skeleton that's capable of a paralyzing touch and summoning rats, and is vulnerable only to silver and magic.

2 HD, AC 5, Atk 1d6 or special, Number Appearing 3d6-2. 
Special: must transform into a hideous monster to use special attacks, touch (save or paralyzed for d6 rounds), summon (call d100 rats, 3 times/day).

d30 Variations - Save vs Dragon

Bandits
Bards
Berserkers & Barbarians
Chimeras
Dinosaurs  
Dragons
Dwarves
Elves 
Fiends
Ghouls & Ghasts
Giants
Gnolls 
Goblins
Hauntings
Jellies Oozes Puddings & Slimes
Kobolds 
Minotaurs
Mummies
Orcs
Paladins
Plant Monsters
Rats
Sea Creatures
Skeletons
Snakes
Spiders
Troll Mutations
Wizards 
Worms
Zombies

BONUS - Treasure Maps 

EXAMPLE - Runed Skeleton, immune to divine damage, weapon: short sword (1d8)
 AC 7, 1 HD, Atk  1d6 or by weapon, Number appearing 3d4, Save as Fighter 1, Morale 12, Treasure nil, Alignment Chaotic.