Thanks! I'll pick up "The Colour of Magic" this weekend. I'm now remembering that I've read "Good Omens" that he did with Neil Gaiman, and I made a note back then to start exploring Discworld, but never followed through with it. Time to fix that.
I'm also a bit less fond of "The Colour of Magic" since I think his writing style was weaker in his first few books and since his characters were not well established. Both "The Colour of Magic" and "The Light Fanstastic" are very fun books but not quite at the same quality level as his later ones once he found his rhythm and built up his world.
I personally find any novel in the Witches arc a lot more enjoyable, starting with "Lords and Ladies". Other good ones: "Carpe Jugulum", "Equal Rites".
Another very enjoyable set is the night watch arc. Both "Guards, Guards" and "Night Watch" are excellent.
[edit]: oh yeah, and how could I forget: "Small Gods". Hilarious even if it stands a little aloof of the rest of the discworld stuff.
But he didn't hit his stride for a few books, and there are many sub-series to read. For a good stand alone, my favorite is Small Gods. You could also read Equal Rites or Mort. Another great story arc starts with Guards! Guards!