None. I will probably never buy a book again when I have the Internet at my disposal.
We're going to have to agree to disagree on this one. Books are still incredibly useful. For one thing, they are generally written by experts. Plenty of people claim to be experts on forums and websites, but you have to be cautious. With authors, many of them have degrees (not that this is a must, but it shows you their dedication and commitment to the field) and usually decades of experience. Sure, you can't talk to them or ask them questions - but by reading what they have to say, you extract valuable knowledge, not just the answers to your burning questions. And sometimes listening (or in this case reading) without asking questions is a good thing!
For another thing, they are written with some chronology. If you get a basic "how to" reefkeeping book, you'll see from start to finish the progression of an aquarium. This is difficult to find in a combination of websites, forums and online articles. You would have to piece together a lot of these to come up with something like The Conscientious Marine Aquarist (423 pages, so more of a reference book). You can get it used for about ten bucks.
Speaking of reference, here's a book called A PocketExpert Guide to Marine Fishes: 500+ Essential-To-Know Aquarium Species:
http://www.amazon.com/PocketExpert-Guide-Marine-Fishes-Essential/dp/1890087386
A book like that could be very helpful for you in stocking your 125 gallon tank. Again, 447 pages. It would take you forever to find that much information on the internet. Again, around twelve bucks.
My guess is you haven't picked up a book lately. You should really try going to a major bookstore and browsing the aquarium section. For one thing, you're bound to get inspiration from the pictures. Many of them break it down step by step, from gathering the equipment to fully stocking the tank. One such book is The New Marine Aquarium: Step-By-Step Setup & Stocking Guide, by Michael Paletta. This book is only $7 used, including shipping. That's less than you probably spent on iTunes this week
The internet is amazing, no doubt, but it is definitely not the only resource...and when you're just starting out, it's important to build a foundation of general knowledge. It will save you a lot of money and heartache if you know more than just what directly applies to what you want to accomplish. There is no better way than starting with quality information to begin with! Set up in such a way that even the person who doesn't know what questions to ask, gets answers.