PC Gamer has demo of MC available.http://www.pcgamer.com/2011/04/19/download-the-minecraft-demo
"Minecraft now has a demo. Procrastinating excavators: you no longer have an excuse for skipping our favorite open-world game. Better yet, it has branded cows that Notch made for us. Keep in mind that these animals are specially-programmed to act as voodoo cows: when you punch them, each PC Gamer editor feels a mild thud in their chest. Be gentle."
"The demo is generous: every tool, mineral and item is accessible, and you can dig, frolic, and build in your world for 90 minutes before it “locks” and becomes uneditable. You can create as many new worlds as you’d like. Let us know what you’re making–send us a screenshot of your demo world to firstname.lastname@example.org