Two big KDE releases are out today: version 4.1.4 and a first release candidate of version 4.2. Version 4.1.4 contains a large number of bug-fixes, particularly to KMail, Okular (PDF) and KGpg (full changelog here). Source downloads and links to binaries (Ubuntu only at present) at the info page.
The 4.2 release candidate contains significant enhancements over version 4.1, including many new features in Plasma and in the supporting applications, improved Python and Ruby scripting and improved support for non-Linux operating systems (BSD, Mac and Windows). See the info page for source downloads and various binaries (Ubuntu, Fedora 10 & Rawhide, OpenSUSE and Magic Linux at present).