My boys got some Legos for Christmas (of course!), and my 7-year old brought me the brochure that came with his set and said, "Dad, go to legoshop.com!" I obliged and he, my three-year old, and I had fun looking at the expensive Death Star and Millenium Falcon sets for a while. Then we poked around some more and discovered the Lego Digital Designer, which is a very cool program. It basically let's you build with Legos on your computer in 3D--kind of a little Lego CAD program. Finding pieces is much easier than digging through the big pile on the floor. You can rotate views, zoom in and out, and play to your heats content. You can also take screenshots of your designs, print them out, or even send your designs to Lego and they'll box up all the pieces needed for it and sell the kit to you. Genius!
It gives you some base models you can use to get started. My boys liked starting with those and they had a lot of fun just discovering the pieces that were available and how they fit together. This expands their collection a lot, and Mom doesn't have to worry about our one-year old finding small pieces on the floor to eat. Here's a screenshot of one of their creations:
You gotta love the disembodied heads.
The widoze software (there was a Mac version too) runs under wine on my two Gutsy Gibbon boxes (one for each boy, luckily). The fast Core 2 Duo machine seems to have no problems with it, but it locks up the old Celeron machine at frustrating times. Overall, It's really fun to play with. I'll probably have to install it on my laptop too so I don't have to fight my boys for time to play.