Here is a comprehensive list of all of Terry Pratchett's books!
The Light Fantastic
Equal Rites
Mort
Sourcery
Wyrd Sisters
Pyramids
Guards! Guards!
Eric
Moving Pictures
Reaper Man
Witches Abroad
Small Gods
Lords and Ladies
Men At Arms
Soul Music
Interesting Times
Maskerade
Feet of Clay
Hogfather
Jingo
The Last Continent
Carpe Jugulum
The Death Trilogy
The Pratchett Portfolio
The Colour of Magic Graphic Novel
The Light Fantastic Graphic Novel
Mort: A Discworld Big Comic
Soul Music Illustrated Screenplay
Wyrd Sisters Illustrated Screenplay
Discworld Quizbook: The UU Challenge
The Discworld Mapp
The Streets of Ankh-Morpork
A Tourist Guide to Lancre
The Science of the Discworld
Discworld GURPS
Wyrd Sisters - The Play
Mort - The Play
Maskerade - The Play
Guards! Guards! - The Play
Men at Arms - The Play
Wyrd Sisters
The Dark Side of the Sun
Strata
Truckers
Diggers
Wings
The Bromeliad (Nome Trilogy)
Only You Can Save Mankind
Johnny and the Dead
Johnny and the Bomb
The Unadulterated Cat
Good Omens
Johnny and the Dead - The Play