I recently signed up for O'Reilly's Safari Books Online which is an online book service providing complete titles from O'Reilly and several other technology book publishers. O'Reilly, if you didn't already know, is one of the leading publishers of technology books. You've seen their books in the Computer section of your local mega-chain bookstore -- they're the ones with the pictures of ducks and chickens and badgers and snakes on them.
Safari Books Online contains, as far as I can tell, the complete lineup of O'Reilly books and titles from other publishers such as Microsoft Press, Que, Manning (think pictures of swashbucklers and jesters), Prentice Hall, and Adobe Press to name a few. As I write this, there are over 6,100 books available. Full books. Complete with indexes, tables of content, and errata.
Having browsed a little bit through everything that's available, my current "Favorites" lineup includes Beautiful Code, MySQL - Fourth Edition, Building Web Services with Java, Programming Python - Third Edition, and A Designer's Guide to Adobe Indesign and XML.
In addition to books, there is other content available such as articles and videos. The videos were a big suprise and now are my favorite feature of Safari. I've been watching Java Fundamentals LiveLessons I and II (14 hours!) by Deitel & Assoc., Working with Color by Bruce Heavin, and Inspired CSS by Andy Clarke. Videos are availabe in both Flash and Quicktime format, and stream reasonably well (though not as well as I would like at times). Video learning is the fastest way I've found to soak up information without falling asleep or becoming distracted.
The best part of Safari: it's only $42.99 per month for a wealth of information at your fingertips. There are cheaper versions of the service ($23 - 40) called "Safari Bookshelf" in which you have a fixed number of slots (10, 20, or 30) that you can fill with books. But the Bookshelf service only includes limited access to the service and requires that you think about which books you'd like to take a look at. With "Safari Library" being complete for $43, it's the no-brainer choice.
Just today I had to do some mucking with a BIND server and instead of Googling my brains out or trying to read documentation written by programmers, I simply went to Safari and checked out DNS and BIND, 5th Edition and DNS and Bind Cookbook. These are books that I would love to have on my bookshef for just this occasion, but I don't work with BIND enough to warrant purchasing them. (Did I mention that you also get up to 35% off when purchasing a print book from Safari?)
Enough raving, the service does have its flaws.
First, reading online is hard on the eyes and simply not as comfortable as kicking back with a book. While Safari does provide an index and table of contents for every book, it can't touch flipping through real pages for ease of use.
Second, the reading experience is somewhat hampered by the intentional limits imposed by the services. For instance, you can only read one section from a chapter at a time, and you have to click the "Next" button to proceed onward. This means that you're reading the books in what are essentially little snippets which can really slow you down. Some books are actual scans and they only let you see one full page at a time. Thus if there is a corresponding photograph on the next page, you have to click "Next" to get to it (there's a photography book I'm reading and I find myself clicking the Next and Previous buttons all the time to switch between the text and images). All of this is made worse by the semi-ajaxy implementation -- there is nothing to indicate that the next page is loading after you click, and browsers like Firefox do not know how to scroll up to the top of the page when you flip to the next page.
Third, the service is kind of slow. Not unusable slow, but noticable 1-2+ second page loads slow. When you're only given a snippet to read at a time, those seconds really start to add up.
All the negatives aside, Safari is great. Having access to this amount of great information is simply amazing.