Focus stacking is a technique in which one takes multiple shots of the same scene at different focus distances, then merges them together to create a final photo that is as sharp as possible from front to back. This helpful tutorial will show you how it's done.
Coming to you from Andrew Marr, this great video will introduce you to the idea of focus stacking in landscape photography. While using the hyperfocal distance is often a great way to get a maximal area of sharpness across an image, if you want absolute maximal sharpness across the entire image, set your lens to its sharpest aperture (normally 3-4 stops above its maximum aperture — f/8 is a good bet) and use focus stacking instead. You might wonder why you wouldn't just stop down further, but beyond f/16 or so, you're going to start seeing noticeable softening from diffraction. This is when focus stacking saves the day. It's a particularly good option if you're looking to keep prominent foreground elements well in focus as well, and as you can see, it's often not particularly hard to do (Photoshop can even automate the process for you). Give it a try!