Slashdot reported on the Opte Project. It's a single guy who's mapping the Internet using code he wrote. Commercial companies like Lumeta provide much more enhanced functionality, but this is still a cool hack.
The Slashdot thread features commentary by Hal Burch and Fyodor, and a useful summary of similar projects. The image at left is supposedly "1/5 of the Internet," but as one Slashdot reader mentioned, it looks a lot like a brain! Given Google has replaced the brain of many people, I imagine this image is appropriate. :)