I've talked about the Entertainment Book before here on the HTN, and while I definitely believe it has hundreds of dollars in savings, I also think you should get the best darn price available for it. Today I found an offer that brings the total cost down to $16, which is the best price we'll probably see until they get marked down halfway through the year (the 2011 edition just came out in November).
First, you'll need to be a member of Ebates - that's my referral link (it's free to sign up and you get a $5 bonus for joining). Once you've logged in, go to the Entertainment.com page and you'll see that the current promotion is for 30% off and 35% cash back! That brings the cost of, say, the Seattle book down from $35 to $24.50, and you'll get 35% cash back on the lower price, or about $8.50. $24.50 - $8.50 = $16! (Plus, you'll get that extra $5 bonus if you're a new member.) Just make sure to click through using the orange "Shop Now" button so your purchase gets credited.
If you want to know more about Ebates, here's a full post with all the details, but in a nutshell, it's an online cash-back rewards program that pays out quarterly checks to you. If you shop online regularly like I do, make a habit of going through Ebates and hassle-free cash back can be yours!