If your intention is to find a recipe here, a recipe there, then searching online should work fine for you. I realize that some people have little desire to cook at all, and may only occasionally need to know a recipe.
But if your intention is to learn more about cooking, then I think a book would help you more. I used to think my mother was very strange for sitting around reading books about cooking. Now, I understand. Like anything, if you want to get better at it, really get better, then you would greatly benefit from some time spent reading. Then, head to the kitchen and practice what you read.
Another advantage of a book is having a compilation of advice from a chef you trust. Sure, you can search online and find a highly-rated recipe for just about anything. But what if you want to learn about quick meals in general? or Mediterranean, Mexican, vegetarian, or Indian dishes? or have a few dozen salad ideas all in one spot? I have found it infinitely useful to be able to pull a book off the shelf, knowing it is a trustworthy compilation, and find what I'm looking for, right there.
- A reference for basic information on just about everything: the Joy of Cooking is the classic reference. Joy is a fairly exhaustive reference, including countless recipes along with (importantly) much explanation of how and why they work. Each section (and subsection!) has an "about..." area that has provided much of my cooking knowledge. Reading this book is like stepping inside my mother's and grandmother's mind.
- Two simpler all-inclusive reference books would be Betty Crocker's Everything You Need to Know or Better Homes and Gardens. I think only one of those two is necessary.
- To learn about cooking techniques, a great starting place is Alton Brown's I'm Just Here for the Food. To get more in depth, you may want to check out something like The Professional Chef.
- To learn about baking bread, check out Artisan Bread in Five Minutes a Day or Peter Reinhart's The Breadbaker's Apprentice.
- Learn about the science behind cooking: Michael Ruhlman's Ratio is my new wish-list book for this topic. Want to create your own muffin recipes without having to build on someone's else's? This book will teach you how. This book contains information on doughs, stocks, sausages, and custards, and I can't wait to read it! Or, check out McGee's On Food and Cooking.
Go-To Books for Specific Cuisine
Besides having reference books like those, I think cookbooks are useful for having a single, trustworthy source on any given topic. Over on the right margin, you can see what's on my shelf, under "Bookshelf."
I don't have an overly extensive cookbook collection, and that's intentional. I would rather get very good at a limited number of dishes, with brief explorations into other areas, than be in a continual state of experimentation. I simply do not have the time to make a new recipe each night, as I have found that it takes me almost twice as long to make a new recipe as it takes me to make one I'm familiar with.
My advice to you is to pick up a couple of books that cover food genres you enjoy, and learn from them. Two of my favorite books are Rachael Ray's 30 Minute Meals and 500 Best Ever Recipes: Mediterranean.
When I need an easy recipe, I go to Rachael Ray... and when I want something new and am willing to put some time into it, I flip through my Mediterranean book.
What About You?
What are the books you find yourself continually coming back to? Where do you turn when you need to learn about a new technique or are looking for ideas?