Am no follower of the Pomodoro technique nor do I know its specifics but before you go ahead and try out those multiple Adobe AIR applications or use the GNOME-oriented Workrave, please try out this software called RSIBreak which was built for KDE specifically.
It isn’t a full fledged timer feature but I think it will get your needs covered with its offerings easily enough. One of the amazing utilities I’ve used, built with KDE Libraries. It should be available in your Linux distribution’s software repository too.

Relax? For a whole 20 seconds?! If there’s something wrong with my computer, there’s no way you’re getting me to do that
the_madman
7 May 10 at 9:50 pm
But when you work, things generally aren’t supposed to go wrong, and if it does go south a moment of thought could be nice!
(P.s., hit that red button to dismiss it in emergency cases)
Harsh
7 May 10 at 10:31 pm
I used kteatime to create a very rough pomodoro app really in its infant stage… Now how am I going to share that
ruurd
19 Sep 11 at 2:34 pm
ruurd – Publish on kde-apps.org? Over github.com? A wordpress.com or blogspot.com blog? I’d sure love to check it out!
Harsh
19 Sep 11 at 9:26 pm