The two-mile challenge
According to these guy's statistics, 40% of US urban travel is 2 miles or less. The site uses Google Maps to draw a 2-mile circle around your address, and challenges you to substitute bicycle trips for car trips to destinations within that circle. It'll also provide a list of places to ride--grocery stores, coffee shops, banks, parks, public transport, and more--all within 2 miles of your address.
Personally, I'm just as prone to walk as to ride for a large fraction of those trips--there's a lot within 1 mile of my apartment. And my own ride-versus-drive decision has a lot more to do with things like how much stuff I'm expecting to bring home and whether there's a secure place to lock up my bike at the far end, than it has to do with whether the destination is close. But still--the mapping tool is cool, especially with the possible-destination list, and I figure that anything that encourages people to ride rather than drive is a good thing.