Lonely Planet Books: Buy 1 Get 1 Half Price (Free Shipping Too)
The US Lonely Planet store has an offer running on their excellent guidebooks at the minute. If you buy 1, you get the 2nd guide book for half price. Plus, there is currently free shipping to Canada, with no minimum spend.
Just add 2 books to your shopping cart, and you will see the discount appear, 50% off the lowest price book.
I have bought quite a few Lonely Planet guides over the years. The most recent was the Iceland book, which I used quite a lot on my trip last month. I find they're excellent for telling you all the little tips about the place. I'm going to Vegas for Christmas, so seriously contemplating getting the Lonely Planet Guide for Las Vegas before I go.