Klingons
DW-World.de, Ex Astris Scientia - Galleries - Klingons, House of Kasara, House of Ku'vaj, K'Tesh's Klingon Recipe Pages, Klingon Imperial Diplomatic Corps, Klingon Imperial Weapons Guild, Klingons, StarTrek.com: Library: Klingon Culture, The House of Veska
Romulans
Ex Astris Scientia - Starship Gallery - Romulans, Information on the Rihannsu, McGuinness Rihannsu page, Romulan Butterfly, Romulan Database, Romulan Information Center, Romulans, Romulus, Sarvok's Rihannsu Web Page
Vulcans
Center for Vulcanism for Humanity, Ex Astris Scientia - Galleries - Vulcans, Vulcans - Star Trek Fans, Vulcans: Demi-Gods or Greeks?
Andorian Dictionary
A dictionary of the Andorian language, cultural notes and description of the blue skinned aliens.
Lost races of Star Trek
The races from TOS that were never seen again.
The Breen System
Includes information on the physiology and technology of the Breen plus an exhaustive listing of every Breen appearance and reference in Star Trek.
To Seek Out New Life
Companion web site to the book that discusses the biology of Star Trek.