Save money - get the book before you go
I made the mistake of heading down to Chile with one travel guide that was better for its photos than anything else. Taxes on imported books in Chile are prohibitively high, so if you thought that Lonely Planet book was expensive in the US, don't even think of stepping into a bookstore in Chile. Have a comprehensive guide with you before you arrive. While it's not a book, I find that browsing photos on flickr can give you a good idea of the vibe a country before you even set foot on its soil.