Right now Kentico CMS partners can login to the Partner Portal and download the beta version of Kentico CMS 6.0. The beta of 6.0 is intented for testing only.
I'm downloading/installing it right now, and I can't wait to get it up and running to see all the new features. For more on what to expect check out the great post by Jeroen Furst a Kentico MVP and his review of the 6.0 CTP.