Terry Pratchett fans - ideas for a book for my DP

[iwouldgoouttonight]

DP loves Terry Pratchett books so thought I'd him get one for christmas but I'm a bit bemused by just how many books he's written! DP seems to have about ten books (all part of something called Discworld?). I've like to get him a book that isn't part of a series so he can read it on its own - does anyone have any recommendations? I've looked on Amazon and there are so many recent titles and I can't work out whether they're part of a series or not!

Dh likes Guards! Guards! best, followed by going postal. He ahsn't read movies movies yet but i think he will like that a lot.

Agree about the in jokes, but that can come gradually over years

Agree Pyramids and Small Gods are in a class of their own but I love anything with Sam Vimes (he's even cool in Monstrous Regiment.) I find Rincewind very tiresome.

BTW I reckon any TP fan would enjoy this.