On a more serious note, assuming that they could fit 250 monsters (plus 50 animals, normal and dire, in an appendix) in it- rumor has it that 300 is the number of critter that they're shooting for- this is a taste of what I'd like to see (off the top of my head):
Aarakockra
Aboleth
Algoid
Allip
Amphisbaena
Ankheg
Animal lord (template)
Ant, Giant
Apparition
Archon, hound
...sword
...tome
Ascomoid
Aurumvorax
Banshee
Basilisk
Bee, giant
Beetle, giant bombardier
...giant fire
...giant slicer
...jishin mushi (earthquake beetle)
Behir
Beholder
...elder orb
...gauth
...observer
...spectator
Belker
Brain in a jar
Brownie
Bugbear
Bulette
Catoblepas
Centipede, giant (multiple sizes)
Chimera
Choker
Cockatrice
Darkmantle
Death knight (template)
Deathbringer
Demon, Balor
...Chasme
...Demogorgon
...Glabrezu
...Graz'zt
...Half-Demon (template)
...Hezrou
...Juilblex
...Manes
...Marilith
...Nalfeshnee
...Orcus
...Succubus
...Vrock
...Yeenoghu
Derro
Deva, Astral
...monadic
...movanic
Devil, Asmodeus
...Baalzebul
...Barbed
...Bearded
...Belial
...Chain
...Erinyes
...Geryon
...Half-devil (template)
...Hellcat
...Horned
...Lemure
...Mephistopholes
...Pit Fiend
...Spined
Disenchanter
Dragon, Black
...Blue
...Green
...Red
...White
...Tiamat
Dragon, Brass
...Bronze
...Copper
...Gold
...Silver
...Bahamut
Dragon, Cloud
...Faerie
...Shadow
Dryad
Dwarf (including most subraces)
...Duergar (separate entry)
Elemental, air (various sizes)
...earth (various sizes)
...fire (various sizes)
...water (various sizes)
Elf (including most subraces)
...Drow (separate entry)
Ettercap
Fiendish creature (template)
Fly, giant
Genie, dao
...djinn
...efreet
...jann
...marid
Ghost (template)
Ghoul
...ghast
...lacedon
Giant, cloud
...fire
...frost
...hill
...mountain
...stone
...storm
Gnoll
...flind
Gnome (including most subraces)
...spriggan (separate entry)
Goblin
Golem, bone
...clay
...flesh
...iron
...stone
Grell
Halfling (including most subraces)
...Jerren (separate entry)
Hell hound
Hobgoblin
Invisible stalker
Intellect devourer
...ustilagor
Iron cobra
Jackalwere
Kobold
Kraken
Kuo-Toan
Leviathan
Locathah
Lurker above
Lycanthrope (template)
Manticore
Meenlock
Medusa
Merfolk
Mimic
Mind flayer
...ulitharid
...elder brain
Nightmare
Nixie
Nymph
Ogre
Ooze, black pudding
...gelatinous cube
...green slime
...grey ooze
...mustard jelly
...ochre jelly
...olive slime
Orc
Owlbear
Para-elemental, ice (various sizes)
...magma (various sizes)
...ooze (various sizes)
...smoke (various sizes)
Pixie
Planetar
Purple worm
Quickling
Rilmani, argenach
...auromach
...cuprilach
...ferrumach
Rust monster
Sahuagin
Scorpion, giant (multiple sizes)
Shadow
Shambling mound
Shrieker
Skeleton (template)
Slaad, blue
...death
...green
...grey
...red
...Ssendem
...Ygorl
Solar
Spawn of Kyuss (template)
Spectre
Sphinx, andro-
...gyno-
...hieraco-
Spider, giant (multiple sizes)
...phase
Spider eater
Sprite
...sea
Tabaxi
Thoqqua
Umber hulk
Unicorn
Vampire (template)
Violet Fungus
Wight
Will o' the wisp
Winter wolf
Worg
Wraith
Wyvern
Xorn (various sizes)
Yellow musk creeper
Yellow musk zombie (template)
Yugoloth, mezzo-
...nyca-
...ultra-
Zombie (template)
...And that's just off the top of my head! I'm sure I could fill that list out pretty well if I put my mind to it...
