After some research and trial and error I finally found the best tea making device.
It's a Bodum Assam teapot. It has two advantages over the clay teapots. First of all it's clear. It makes it very easy to judge the strength of your infusion. Second, the french press like plunger filter stops the infusion process, yet you don't have to take out and discard tea leaves immediately. One drawback might be that the tea cools down faster than in a clay pot, but I actually like cold tea.

By the way, I highly recomend Kitchen Kapers. I buy a lot of my kitchen gadgets from them.