My first Discworld novel was Mort, and i absolutely loved it. Haven't even thought about it in years. In fact i'm going to go and start re-reading it right now!
p.s. i got a copy of 5th Elephant signed a few years ago, and Terry wrote "with respect and Garlick". This has always confused me, and I just assumed he was being deliberately surreal. Part of me has always wondered however, if i was simply missing the joke. If this makes sense to anyone who knows Discworld/Pratchett novels better than me, please let me know.