Here's a fresh new idea for a bike lock: the TiGr. It's a titanium "bow" that straps around your bike and secures it to anything nearby.
The lock can stay stretched along the top of your bike's frame most of the time, and when it's time to lock up this lightweight device can strap around anything up to 5.5-inches wide. It's supposedly resistant to cutting, which is a plus with bike locks. It's currently a Kickstarter project in need of funding, so if you like this idea, go toss 'em some cash to make it a reality.