Ahh, Spain. I love Spain. It's so saucy, filled with 3pm siesta's, sangria, and tasty food. I have only visited briefly on a stint to Barcelona during one of my European adventures. I fell in love, and you will, too after you check out the DK Eyewitness Travel Guide which will prepare you for your own trip better than any guide I've read to date.
This resource just came out in March so it is fully updated and ready to help you explore this gorgeous country, wherever you decide to visit. DK even gives you sample two day trips (and longer) of different cities like Barcelona and Madrid, so that you can get the most out of your adventure, even if you are short on time. You also get a bit of a history lesson on architecture, agriculture, art, animals, environment, etc.. which is kind of nice because you'll be semi educated before your trip. There is A LOT of information so give yourself enough time beforehand to read through it all.
This guide is PERFECT for those of you who want to see everything and really experience the culture, but don't even know where to start.