While checking out the stamping and scrapbooking section of my public library, I ran across this book: The Encyclopedia of Greeting Card Tools & Techniques by Susan Pickering Rothamel.
In addition to the great info, there are lots of inspiring samples. You can a lot by reading the book but you'll also be inspired just looking through the samples. There are also biographical entries for several stamping professionals (including Dee Gruening, whom I used to watch on the Carol Duvall show years ago) which also feature examples of their work. The book also includes tips on card composition and card submissions.
Check it out!