We love keyboard shortcuts, and we love Gmail. This minimalistic Gmail cheat sheet brings the two together, visually highlighting the shortcuts that will help you use Gmail faster and easier.
Of course, if you have keyboard shortcuts enabled in Gmail (you have to go into your settings to turn them on), you can hit the question mark (?) for Gmail's own pop-up keyboard reference. This cheat sheet, however, is a great visual reference, which might make learning and understanding the shortcuts a bit easier. Also, you can save it to your desktop or post it in your office for a quick look every now and then.
Here it is for you to save (by right-clicking on the image):