I checked out 3-4 books from the local library when I got my WSM, and two of them included the Weber Smoke and the Smoking Meat by Jeff that Chris mentioned.
I liked the Weber one a lot, but they split the recipes between gas grills, the charcoal grills, and the smokers. Not that you can't improvise and figure out how to adjust anyway, but they very much try to have various recipes that would work well across all the weber products.
For JUST WSM recipes I really liked the Smoking Meat one by Jeff Phillips the most. Of those two and two others I checked out I ended up buying a permanent copy of the Smoking Meats.
If you have a tablet (or actually I think you can just a kindle app for a pc or laptop, I might be wrong) look for sales on the electronic editions if you like that route. I usually prefer the real book for things like this, but in this case they had the Smoking Meats on sale for Kindle for $2.99. I jumped all over that. So to be fair, one of the reasons I bought the Smoking Meats on is because it was just $2.99 at the time. But I think I would of bought it at the hard copy price if the Kindle version wasn't on sale.
My advice - check a few out from the library, see which ones you like, then purchase a copy if you find one you think you will want to refer back to.