I heard about a raised bed called a Lasagna Garden this spring. Not much more than sheet composting, but was ready in about 6-weeks. NO DIGGING!!! A thick layer of wet newspapers, like 3 or 4 inches, and then layers of compostable organics. Soak it well and cover with a tarp.
There are some notes and photos on my blog at http://www.compostcritter.com. The big one was build right on top of the grass on very rocky/clay soil… plants did great first season, and NO weeds and no grass coming through. ( one was over an excavation project for my septic (ugh).
For the winter I layered them again and am letting them go. Will soak and cover for a few weeks to let them cook again. An trying to see if I can capture any winter solar heat with trashbags of sand on some of the beds.