At the moment, there are only two semi up-to-date x86-64 (that is, for Athlon-64, Intel EMT64, and Opteron) Debian-based live CDs.
- Knoppix-64, based on Knoppix 3.4 (somewhat out of date as Knoppix 4.0 is out)
- Ubuntu, which is kept up to date and is available tucked away on their FTP site
I’m getting Ubuntu now to try out on my new workstation.