Minecraft's alpha phase is ticking to a close, with a beta - and price change - due on 20th December. It'll cost €14.95 from that point on. Notch says: "With Beta comes a larger focus on polish and content, and we’ll start early on with adding proper modding support with a stable API," and also "We will also change the license to remove the line that promises all future versions of the game for free. Please note that this change only affects people who buy the game after December 20, so if you got the game for during alpha, you will still get all future updates for free, despite this change."
But, presumably, you've bought it already.