It's arriving a week later than scheduled, but KDE 4.3
is now available. KDE 4.3 contains many improvements for Plasma, enhanced KWin effects, Dolphin effects, many application improvements, and much more.
An extensive overview of the changes for KDE 4.3 can be found at KDE.org
within their release announcement. The next major release of KDE 4 will be the 4.4 release to come next January, but in the meantime there will be monthly point release updates for KDE 4.3.