The latest kernel version for testing is indeed, 2.6.8, If you switch to testing (replace in /etc/apt/sources.list all the "testing" entries to "unstable" that is) you'll see that the latest version is 2.6.10.
However, this represents the latest versions of the kernel that Debian has applied patches to and which is available from Debian. They'll always be a bit behind (it's a good thing though) with the latest kernel version.
But, if you really want the latest version and you have the time and skills to configure & compile a kernel from source, follow the link J.W. gave to you.
And indeed, good luck!