I found this on the web today...
LEGO Digital Designer
You can literally design ANYTHING with LEGOs in 3-D.
The software is completely free and really easy to use. I loved LEGOs as a child and this is just TOO COOL!
Here's the real kicker. Once you've completed your masterpiece you can upload it to the LEGO Factory website (http://factory.lego.com/) and purchase a kit that contains all of the bricks that you used to assemble your virtual creation so you can make it for real!
I can see how my weekend will be spent... LOL