Based on my visit in August (review in the works) and browsing the gallery afterward as well as checking @geomorph 's list and the news thread, here is an incomplete list of species formerly held at the Denver Zoo:
Predator Ridge
Cheetah
Banded Mongoose
Hoofstock Yards
American Bison
Musk Ox
Dromedary Camel
Common Eland [?]
Secretary Bird
Northern Shores
Polar Bear
North American River Otter
Primate Panorama
Common Squirrel Monkey
Black-Crested Macaque
Lion-Tailed Macaque
White-Eared Titi
Giant Elephant Shrew
Emperor Tamarin
Mongoose Lemur
Pygmy Marmoset
Red-Crowned Mangabey
Monkey Row
Wolf's Guenon
Silvered Leaf Langur
Hanuan Langur
Tropical Discovery
Howler Monkey
Green Anaconda
Sheep Mountain
Dall Sheep
Bear Mountain (defunct)
Asiatic Black Bear
Coati
Feline Building (defunct)
Amur Leopard
Fossa
Snow Leopard
Dwarf Mongoose
Several
Northern Tree Shrew
Red Panda
Maned Wolf
Bird World (defunct) - entirely credit to @geomorph
Stellar's Sea Eagle
Kea
Double-wattled Cassowary
Snowy-headed Robin Chat
Crested Wood Partridge
Shama Thrush
Scarlet-faced Liocichlas
African Pygmy Falcon
Micronesian Kingfisher
Tawny Frogmouth
Hawk-headed Parrot
White-eared Catbird
Blue and Gold Macaw
Blue-crowned Laughing Thrush
Boat-billed Heron
Golden-breasted Starling
Green-winged Dove
Green-winged Macaw
Hammerkop
Hottentot Teal
Lady Ross' Turaco
Nicobar Pigeon
Pekin Robin
Scarlet-chested Sunbird
Silver-beaked Tanager
Sunbittern
White-faced Whistling Duck
Yellow-breasted Ground Dove
African Pygmy Goose
Blue Dacnis
Hooded Pitta
Luzon Bleeding-heart Dove
Mariana Fruit Dove
Turquoise Tanager
Blue-gray Tanager
Crested Wood Partridge
Golden-breasted Starling
Green-naped Pheasant Pigeon
Jambu Fruit Dove
Paradise Tanager
Spur-winged Plover
White-headed Buffalo Weaver
Rhinoceros Hornbill
Boat-billed Heron
Common Piping Guan
Crested Oropendola
Hammerkop
Inca Tern
Ringed Teal
Rothschild's Peacock Pheasant
Storm Stork
Two-toed Sloth
White-faced Whistling Duck
Egyptian Plover:
African Pygmy Goose
Chestnut-backed Thrush
Mariana Fruit Dove
Pileated Woodpecker
Spur-winged Plover
Three-toed Box Turtle
Yellow-breasted Ground Dove
Blue-crowned Motmot
Green Wood Hoopoe
Tawny Frogmouth
Violaceaous Euphonia
Blue-breasted Kingfisher
Green Aracari
Red-legged Honeycreeper
Cinereous Vulture
Laughing Kookaburra
Palm Cockatoo
Red-legged Seriema
Toucan
It is possible one of the langur species listed is still at the zoo as one habitat was labelled a 'Gibbon-Langur Habitat' but the animals were off-display and there was no detailed signage. I assume the buff-cheeked gibbons were off-display there; a keeper did clarify they were not white-cheeked.
I may be incorrect about the placement of the Cheetah.
Predator Ridge
Cheetah
Banded Mongoose
Hoofstock Yards
American Bison
Musk Ox
Dromedary Camel
Common Eland [?]
Secretary Bird
Northern Shores
Polar Bear
North American River Otter
Primate Panorama
Common Squirrel Monkey
Black-Crested Macaque
Lion-Tailed Macaque
White-Eared Titi
Giant Elephant Shrew
Emperor Tamarin
Mongoose Lemur
Pygmy Marmoset
Red-Crowned Mangabey
Monkey Row
Wolf's Guenon
Silvered Leaf Langur
Hanuan Langur
Tropical Discovery
Howler Monkey
Green Anaconda
Sheep Mountain
Dall Sheep
Bear Mountain (defunct)
Asiatic Black Bear
Coati
Feline Building (defunct)
Amur Leopard
Fossa
Snow Leopard
Dwarf Mongoose
Several
Northern Tree Shrew
Red Panda
Maned Wolf
Bird World (defunct) - entirely credit to @geomorph
Stellar's Sea Eagle
Kea
Double-wattled Cassowary
Snowy-headed Robin Chat
Crested Wood Partridge
Shama Thrush
Scarlet-faced Liocichlas
African Pygmy Falcon
Micronesian Kingfisher
Tawny Frogmouth
Hawk-headed Parrot
White-eared Catbird
Blue and Gold Macaw
Blue-crowned Laughing Thrush
Boat-billed Heron
Golden-breasted Starling
Green-winged Dove
Green-winged Macaw
Hammerkop
Hottentot Teal
Lady Ross' Turaco
Nicobar Pigeon
Pekin Robin
Scarlet-chested Sunbird
Silver-beaked Tanager
Sunbittern
White-faced Whistling Duck
Yellow-breasted Ground Dove
African Pygmy Goose
Blue Dacnis
Hooded Pitta
Luzon Bleeding-heart Dove
Mariana Fruit Dove
Turquoise Tanager
Blue-gray Tanager
Crested Wood Partridge
Golden-breasted Starling
Green-naped Pheasant Pigeon
Jambu Fruit Dove
Paradise Tanager
Spur-winged Plover
White-headed Buffalo Weaver
Rhinoceros Hornbill
Boat-billed Heron
Common Piping Guan
Crested Oropendola
Hammerkop
Inca Tern
Ringed Teal
Rothschild's Peacock Pheasant
Storm Stork
Two-toed Sloth
White-faced Whistling Duck
Egyptian Plover:
African Pygmy Goose
Chestnut-backed Thrush
Mariana Fruit Dove
Pileated Woodpecker
Spur-winged Plover
Three-toed Box Turtle
Yellow-breasted Ground Dove
Blue-crowned Motmot
Green Wood Hoopoe
Tawny Frogmouth
Violaceaous Euphonia
Blue-breasted Kingfisher
Green Aracari
Red-legged Honeycreeper
Cinereous Vulture
Laughing Kookaburra
Palm Cockatoo
Red-legged Seriema
Toucan
It is possible one of the langur species listed is still at the zoo as one habitat was labelled a 'Gibbon-Langur Habitat' but the animals were off-display and there was no detailed signage. I assume the buff-cheeked gibbons were off-display there; a keeper did clarify they were not white-cheeked.
I may be incorrect about the placement of the Cheetah.