I just finished Sourcery by Terry Pratchett.

Sourcery is the fifth Discworld novel, before Pratchett really worked his way into the current plot skeleton of adding some modern item to Discworld, with a magical spin.

It's a Rincewind novel, and features him saving the world from magic after a new kind of wizard, an eighth son of an eighth son of an eighth is born and greatly increases the effectiveness of magic.

Like all the Discworld books, it's a fun read.