Long VGA cables exist, but the longer it is, the fuzzier the image will get -- there's no strict limit. The quality of the cable is critical. A good cable will be nearly a 1/2" in diameter. If it's scarcely thicker (and no stiffer) than a power cord, it's not a good cable. Don't expect to be running insane resolutions and refresh rates. (Luckily, LCDs don't require high refresh rates, so that helps.)
USB's official limit is 16 feet, I think. I think I might have done 20 at one point, I don't think it caused problems. Note, however, that this is a maximum between devices, so you can always put a USB hub in between, so that the USB hub is between two 12 foot stretches. USB extenders that use ethernet cable also exist, but are pricey.
tooki