Smooth Tasks (a fork of mbaszczewskis STasks plasmoid) is a taskbar replacement that has window peeking similar to Windows 7 when you use the kwin 'highlite window' effect. Even if this effect is not used you can click the tooltip in order to activate the corresponding window.
Until now you had to compile Smooth Tasks, but thanks to Usoftx, you can use a .deb package for Kubuntu.
Download Smooth Tasks Kubuntu .deb | Smooth Tasks page.
If you are using Gnome, well, you can't use Smooth Tasks but I suggest you try DockBarX which is somewhat similar.
[via ubuntu life]