KDE 4.3 will be released in a week or two, but as a last minute testing version, a third release candidate has made its way out of the K-camp. KDE 4.3 RC3 contains bug fixes, including a notable one that should improve the performance of Plasma. In general, KDE 4.3 integrates several new technologies (i.e. PolicyKit and Geolocation services), new KWin window animation effects, various bug fixes, and many changes to improve the KDE Linux desktop.
The release announcement for KDE 4.3 RC3 can be found at KDE.org