You've probably seen a door, whether wardrobe- or cabinet-sized, that can perform this little trick:

Manufacturers of cabinetry hardware refer to that as a pocket door, and the attendant hardware as pocket door slides. (In overhead applications, where they disappear in the manner of a garage door, they may be called flipper doors and flipper slides.) The nomenclature's a bit confusing, as the term "pocket door" also refers to interior doors between rooms that slide sideways into the wall, Star-Trek-style, so you'll want to be careful if ordering "pocket door hardware" online.

Hooking up a set of pocket door slides is a little more work than installing regular drawer slides--for one thing, you'll need to whip up an extra "follower strip" that attaches to the slides, and the door then hinges to the follower strip--but a dedicated DIY'er should be able to pull it off.

The hardware doesn't come cheap: On the affordable end, a pair of these with 12" to 24" of slide travel runs $45-$50 at Rockler.

Rockler's EZ Pocket Door System Pocket Door Slide

If you're doing high-end work for a client, however, you'll probably want to step up to German manufacturer Häfele's Accuride line of pocket door slides, available at retailers like KitchenSource.com.

Häfele's Accuride system

Häfele's high-end hardware is eye-wateringly expensive: a pair with 12" of slide travel costs $110, and stepping up to 32" of travel will set the client back $135 per pair.

Regardless of the manufacturer, note that these prices are just for the slides--the hinges aren't included.