A Murphy bed helps you save space: Pull it down when you need it, back up when you want to use the room for another purpose. Murphy beds are expensive, though. Make one yourself with IKEA cabinets.
IKEA Hackers member IH guest offers the full instructions for this DIY bed-in-a-closet. You'll be making the bed frame to fit the cabinets, but other than that, this looks like a very doable project if you're handy. The project uses strong door hinges as the mechanism for folding the bed up. It might not be as easy to pull the bed up and down as with a Murphy bed-kit, but you'll save a bunch of money and get a workout.
Hack a PAX Murphy Bed [IKEA Hackers]