So periodically folks will ask me what I can recommend for expanding their understanding of photography. I recently realized I really ought to put this in one place so that I can point to it. It'll save me time and help anyone who asks get a timely and complete answer.
For beginners I would recommend National Geographic Photography Field Guide: Secrets to Making Great Pictures, Second Edition. I have a new edition which is also good, but I still think the 2nd edition is the best version I've spent any time with. It covers the basics, gives lots of good inspiration, and is, of course, loaded with great photos to illustrate principle of composition, lighting, and technique. I've got a link on the sidebar to the amazon listing for this book.
If you get this book you absolutely must, read about shutter, aperture, and film speed, and make sure you read the explanation of depth of field. You need to know how your camera works, and this book does a good job explaining that to you. Finally, the tips from NG photographers are great fun and helpful too.
There are a probably any number of web sites that have these basic ideas explained on them, but not with such good example photos, and not in such detail. The book is really worth getting.
Once you have the NG book under your belt, or even before if you like to skip ahead, you should go over to Phil Douglis's web site and look at his pictures and read his explanations. It's an absolutely dynamite education in creating meaningful images using all the elements of composition, timing, and technique. Periodically I'll go and read look through some of Phil's photos to improve my own composition. His images are very thoughtful. At one point in time I worked through every photo in every gallery on his site. You have to make sure you read his explanations as well.
Eventually, you'll want to understand light. The NG book and Phil Douglis will definitely get you started, but until you start thinking in terms of controlling light you probably won't be thinking about light nearly as much as you should be. The Strobist web site is a great way to wade into the lighting world from the shallow, cheap, and light (no pun intended) end. Even if you aren't to the place where you can buy and use the strobist stuff, read his "Lighting 101" and you'll learn a lot.
So there's a start. I'm sure I'll expand this post as time goes on, and perhaps supplement with other recommendations. The focus of these recommendations is, of course, on the capture end of the process. Today, and really it has always been this way at some level, photography is much more than the capture of images. The eye to see the good ones you got, the know-how to sort them and organize them out of the rest of the mess, and the ability to develop, edit, and deliver them in whatever form they are needed are all part of the process--and that's a story for a different day.