The iPad is a veritable fingerprint magnet - we doubt that's ever going to change. To keep it clean, you'll either need to quit touching it (not likely) or regularly wipe it down with a glass-safe cloth (not likely, either, because you're downright lazy). Here's something more likely to work: the iShine, an iPad sleeve made entirely from a glass-cleaning microfiber material.
Since the sleeve's fabric will take off your slate's prints and smudges, you can use it like a regular cleaning cloth, folding it and wiping everything clean. The clever trick, though, is that intentionally wiping isn't even necessary. Just put the tablet in the sleeve, close up the nylon drawstring, throw it in your bag and let the regular movement of the tablet inside the sleeve do the cleaning all on its own.
Granted, the iShine is a very simple sleeve, so there's not much to expect in terms of protection from bumps and drops (there's no padding whatsoever). The material, PMA 240g microfiber, should handily keep away scratches of any kind, though.
According to reviews I've seen, simply storing the iPad into the sleeve and rubbing it deliberately a couple of times is enough to restore it to a brand new shine. Sounds like an excellent option if you can do without the extra padded protection for your iPad.
Amazon has the iShine for $12.95.
iShine Microfiber iPhone & iPod Sleeve
Sale Price: $5.95