Minecraft

Minecraft has reached 2 million sales !
For those who don't know what is minecraft :
Minecraft is an addictive game in which you can destroy, or creates 1m blocks like sand, rock or wood block.
But what is awesome in that game is that it's an FPS so you can really live in what you build.
Other interesting stuff is redstone wire that allows you to connect things like lamps piston or music box.
Rails are also very fun : you can make your own circuits of minecarts powered by resdstone.
Servers are free : evrybody can host a server, you just need to have bought the game once and its low cost (10€) makes it very affordable.
The community is pretty nice : lots of mods are available and servers are great. The only problem in my opinion is that the game take a lot of resources for the server so it costs a lot to host a simple server.

Here's an example of a city build by players.
The game itself make is very enjoyable to play and to build and you'll not notice losing tons of hours when you play.
But the game is only in beta so it's gonna be way better ! For example, Notch, the director of Mojang plan to add modding support to Minecraft in some updates.
Here is a link to minecraft.net the official website.
Have fun !