To celebrate both the 30th anniversary of the original novel and the release of the new Hitch-Hiker's book, And Another Thing by Eoin Colfer, Pan Macmillan have re-released the original five Hitch-Hiker's Guide to the Galaxy novels in new covers. Most notable about this release is that The Hitch-Hiker's Guide to the Galaxy itself has a blank cover: you yourself can create the cover using a provided assortment of stickers. So if the cover sucks, it's your own fault!
The new editions also come with fresh new introductions by other writers, such as Russell T. Davies (outgoing producer of the new Doctor Who), Monty Pythoner Terry Jones and Neil Gaiman, and a host of rarely-seen publicity photos and press releases from the time of each book's release.
Tying in with the release of Kim Stanley Robinson's very fine Galileo's Dream, HarperCollins Voyager meanwhile are reissuing his classic Mars Trilogy in very nice new covers. Unfortunately, they are also in the larger 'B-format' paperbacks which I know many readers aren't too keen on. However, the books are so great to look at, it's worth the extra inconvenience of their bulky size.
Both sets of book are available in the UK right now.