I finished this one back in December: The intro to this interview with Pratchett says it well:
“Terry Pratchett sells more books than… well… a lot of people. In the United Kingdom, where he was born and now lives and works, Pratchett sells — to put it bluntly — more books than God.”
Here’s a long list of all the Discworld ones anyway.
What is the Discworld, you may ask, not having steeped yourself (overlong, like a bitter cup of tea?) in Pratchett’s prosody?
Most of Pratchett’s books are set in a fantastical world, which is flat, like a pancake, and which rests on the backs of some elephants, which in turn stroll around on the back of a giant turtle which swims through the universe… Things are quirky on the Discworld. Light gets puddled up in valleys and everyone gets a personal chat with Death when they kick it.
Now, I wouldn’t necessarily start out with reading Night Watch, if you’re interested in starting up in the Discworld thing. There are recurring characters and running gags and little bits of continuity which make more sense if you read them in some semblance of order.
I’d recommend starting out with Mort or Small Gods, if not the first and second ones: The Light Fantastic and The Colour of Magic
Other stuff:
A nice fansite with lots of links to pictures and things.
Pratchett interview regarding Night Watch
Ye olde Amazon link.