Wyrd Sisters by Terry Pratchett

[Carla]

Leyland - The first two Discworld books (Colour of Magic and Light Fantastic) aren't the best place to start, in my view. They're a sort of extended spoof on the Epic Fantasy genre, great fun if you read a lot of it and get all the references (especially so if you've also got slightly bored with it), but they don't have much of a plot. Equal Rites also doesn't have much of a plot.

Pratchett says that he discovered the delights of plot round about Book 4 (which was Mort). I think the best place to start with Discworld is one of the books after this point, but still early in the series. The ones I recommend as starting points are:
Mort
Wyrd Sisters
Guards! Guards!
Pyramids
Small Gods

Terry Pratchett had got into his Discworld stride by the time he wrote these, so they are excellent - they have plot and character and sharp commentary as well as all the jokes. They'll give you a good idea of what the Discworld series is like. All of these are either stand-alones (Pyramids, Small Gods) or near the beginning of their respective series, so you don't need to have read any of the others. Guards! Guards! is the first of the City Watch, Wyrd Sisters is the first where the Witches really get going (Granny Weatherwax appears earlier, in Equal Rites, but there's no benefit in having read Equal Rites before Wyrd Sisters).

If you like these, you'll probably like the rest of the Discworld series. The later novels are best read in order, either in publication order or by following first one series and then another, as in the flowchart that Ash linked to. You can read the first three anywhere you like.

Hope this is some help!