The Vimes series is amazing... I think it's a bit above the Moist series but I absolutely love Raising Steam and, to a lesser extent, Making Money - because both characters are coming together. Still, I think my top pitch is somewhere within Night's Watch, Men at Arms & Jingo - I think Guards! Guards! is also quite good but Night's Watch did nearly everything Guards! Guards! did... but did it better.

Honestly, his books are just amazing though, quite worth a read.... possibly skipping to start at Equal Rites since The Colour of Magic and The Light Fantastic were less polished than his later works - but do check out the Tim Curry having movie covering those first two books... maybe bring a power point presentation or two along to appease any power hungry wizards though.