Today one of our “product owners” (or at least close to that role within the organizational structure) overheard me discussing my recent code kata with someone and he linked me to an interesting site full of all kinds of mathematical problems to solve: http://projecteuler.net/.
Now if I ever find myself wanting to do a code kata and have no idea where to stat I can just take a gander at their problems page. 
Hi, in one of my recent blog posts, I collected some sites that contain exercises for katas. Take a look:
http://blog.codecentric.de/en/2010/05/verwendung-von-tdd-in-der-praxis/
Kind Regards,
Andreas
Thanks for the link Andreas!