Tried the newly released Ubuntu 6.06 a couple nights back. Like Knoppix it's a live Linux distribution meaning it can run from CD with no installation required.
It's the first time I've tried Ubuntu and I was suitably impressed. It's more polished and less cluttered than Knoppix, and aimed squarely at the non-geeky user.
Unfortunately like with Knoppix I can only get a maximum screen resolution of 800x600 (although I could install it and then download and install the nVidia drivers), but unlike Knoppix it won't even boot on the other computer so I couldn't try it with an Internet connection.