Years ago, my mom gave me a book called "Everything You Can Buy in Garden Centers." I used it for a long time as I learned the difference between pruners and loppers, spades and shovels, grass rakes and garden rakes. I used the book until it fell apart--and by that time, I knew my tools pretty well.
Now, garden writer and web expert Monica Hemingway has a site called Gardening Products Review. I just wrote a review for GPR on a wonderful digging tool called "Spear Head Spade." It was invented by Daniel Mathieu of Windsor, CT, an octogenarian with bad knees and a love of gardening. It's more like a combination of a spade with a garden knife or axe, which leads me to call it "the sharpest shovel in the shed."
Please visit Monica's site and learn about Daniel Mathieu's invention. It's my new best friend.