Starting with "The Color of Magic" and it's sequel "The Light Fantastic" Pratchett created the Discworld. There are 41 novels about the Discworld, and a lot of additional books. There are a few series of books (based on characters), about Rincewind, Death, Witches and others.
Some of his books were adapted for theatre, many are issued in audio format, there are a few illustrated books, a Discworld "encyclopedia", maps and more.
The first Pratchet's book I have read was "Good Omens". That book was written with Neil Gaimen and it is completely unrelated to Discworld. I really liked the sense of humor, so I started reading every book I could find.
There are also other non-discworld novels. The "Nomes" trilogy (also known as "Carpet People") is a big part about religion. Then there is the series about Johhny Maxwell, which are in a way, books about children for children. At least that is how I see them.
Below is a list of Pratchett novels and books. It is probably not complete, but the idea is to track everything owned and read.
The list shows the transaltions for the books that are available in Serbian. There are little boxes next to the individual version of the books, and the values are H-Have, r-Read. If the cell is empty (actually has an 'x') then I haven't read it yet.
Last revision May 2015.
Various other discworld books
The official Pratchet's page is at www.terrypratchett.co.uk
For browsing around other pages you can start at www.ie.lspace.org and continue further...
Laguna (the Serbian publisher) you can find some info and buy books.