Ireth
Mythic Scribe
After Mort, I'm hoping to read a few things by Gaiman and then cap off Pratchett with Good Omens. I'll probably read Making Money, too, though, because I enjoyed Postal. I want to start doing articles like "What I learned about writing from reading Pratchett" and other authors. The idea is helping to get me to read more.
Come to think of it, I believe you were the one who recommended Going Postal. Is there a Pratchett book you'd add to the list?
The Shepherd's Crown, full stop. It's his final book, and it's amazing. Though it might make more sense if you read a few of the earlier books first, specifically Lords and Ladies and The Wee Free Men (and, actually, the other Tiffany Aching books as well). There are lots of references to those books you might not fully understand otherwise.
I will warn you, though, have Kleenex ready. There will be tears.
Aside from that... Reaper Man has always been a fave of mine (another Death one, unsurprisingly). Hogfather is good too; I read it for Death rather than the wizards. Also Soul Music (though that one involves the wizards a fair bit too, so YMMV), and The Amazing Maurice and His Educated Rodents, and Thud!, and Snuff (though the latter two might not make sense if you skip ahead, since Vimes goes through plenty of character development in the books prior)...
Basically, the whole thing is awesome. Let's just leave it at that. XD
Dark Lord
Acolyte
Shadow Lord
Grandmaster