Of course, I know all concerning the monorail.
Current 2011
Forest - Okapi
Mountain - Nubian Ibex
Woodlands - Grevy's Zebra
Predator/Prey - Red-Flanked Duiker, Caracal
River - Waterbuck, North American White Pelicans, White-Faced Whistling Duck, Fulvous Whistling Duck, White Breasted COrmorant, Blue Crane, White Stork, Hybrid African Yellow-Billed Duck, Goliath Heron
Arid Desert - Scimitar-Horned Oryx, Addra Gazelle
Semi-Arid Desert - Addax, Gemsbok
Scrub - Kori Bustard, Lappet-Faced Vulture, Hooded Vulture, Egyptian Vulture
Bush (part 1) - East African Bongo
Bush (proper) - Greater Kudu, Patterson's Eland, Gerenuk, Thomson's Gazelle, East and West African Crowned Cranes, Marabou Stork, Southern Ground Hornbill, Lappet-Faced Vulture, Ostrich
Forest - Chimpanzees
Original 1990
Forest - Okapi
Mountain - Nubian Ibex, White-Backed Vulture (also Egyptian Vulture later)
Woodlands - Eland, Sable Antelope, Egyptian Goose
Predator/Prey - Gunther's Dik-Dik, Caracal/Black Leopard
River - Sitatunga, Nile lechwe, Eastern White Pelican, Pink Backed Pelican, Goliath Heron, Saddle Billed Stork, African Spoonbill, up to 10 species of ducks and geese, Sacred and Hadada Ibis (also at later dates Blue Crane, White Stork, Abdim's Stork, Yellow-Billed Stork, Guineafowl)
Arid Desert - Scimitar-Horned Oryx, Slender Horned Gazelle
Semi Arid Desert - Addax, Addra gazelle, Egyptian Vulture (also at times Grevy's Zebra, and until recently ostrich)
Scrub - Kori Bustard, Secretary Bird
Bush (part 1) - Gerenuk
Bush - Greater Kudu, Impala, Ostrich, Abyssinian Ground Hornbill, Crowned Crane, Marabou Stork, Lappet-Faced Vulture, Grevy's Zebra
Forest - East African Bongo, West African Crowned Crane, Yellow-Backed Duiker
Proposed species in the original design, but never added
Mountain - some species of Eagle (exhibit originally designed as an aviary)
River - Reedbuck, Waterbuck, Lechwe, Sitatunga, Fish Eagle
Bush - Speke's Gazelle, Beisa Oryx