I used to read his books aloud to DS2.
As well as the Discworld series, he wrote some excellent books for children. If you haven't come across them, please seek them out, as they seem to particularly please boys, and often gets them reading.
Truckers
Diggers
Wings
(3 books about a group of dwarves initially living in a department store)
Also "Johnny and the Bomb" and "Only you can save mankind"
A very talented write with a great mind and well honed sense of humour. He will be missed.