Amarok 2 and Kontact
The Amarok 2 beta is available in Debian unstable as of yesterday (I think). Looks very promising, indeed. Nowhere near finished, but cool and quite functional nonetheless.
I just started the KDE4 version of Kontact the first time and instantly placed it on one of my extra laptop buttons, replacing Liferea.
KDE4 shapes up to be excellent. Though I will probably be staying with Window Maker for a long time (which is a pity, because I never really get to use Martin’s work) I find myself using more and more of the KDE4 applications.