There are lots of inexpensive ways to hang up your bike, most of them involving floor-to-ceiling contraptions. This DIY bike hanger is a simple pair of hooks made from old handlebars you screw into the wall to get your bike off the floor.
If you have an old bike with drop-styled handle bars or can find the parts second-hand, you have most of what you need to make this bike rack. Wherever you want to hang your bike, screw in the handlebars (with attached stem and wall flange) and you've got a convenient holder for your bike.
For more instructions getting your bike off the ground, see Kyle Wilson's step-by-step instructions linked below.
DIY Wall Bike Hanger [The Illustrations of Kyle Wilson]