This is a personal reading challenge that I threw together because I love all things Pratchett. I'll be tracking my progress below. This challenge might stretch into next year, but as all Pratchett fans know, Discworld isn't really about conforming to the rules!
Rincewind Novels and Short Stories
1. The Color of Magic - Completed March 19, 2009
2. The Light Fantastic - Completed April 3, 2009
3. Sourcery
4. (Faust) Eric
5. Troll Bridge (Short Story)
6. Interesting Times
7. The Last Continent
8. The Last Hero
The Witches Novels and Short Stories
1. Equal Rites - Competed May 19, 2009
2. Wyrd Sisters
3. Witches Abroad
4. Lords and Ladies
5. Maskerade
6. The Sea and Little Fishes (Short Stories)
7. Carpe Jugulum
Death Novels and Short Stories
1. Mort- Completed January 2010
2. Reaper Man
3. Soul Music
4. Hogfather
5. Thief of Time
Watch Novels and Short Stories
1. Guards, Guards
2. Theatre of Cruelty (Short Story)
3. Men at Arms
4. Feet of Clay
5. Jingo
6. The Fifth Elephant
7. Night Watch
8. Thud
Ancient Civilizations Novels and Short Stories
1. Pyramids
2. Death and What Comes Next (Short Story)
3. Small Gods
Industrial Revolution Novels and Short Stories
1. Moving Pictures
2. The Truth
3. Monstrous Regiment
4. Going Postal (Moist Von Lipwig 1)
5. Making Money (Moist Von Lipwig 2)
Unknown:
The Unseen Academicals (October 2009)
Good luck! I love Pratchett's Disc World books and have read many of them. One of my favorites is "The Truth."