I bought a Flow Fitness DTM100i Walkingpad. Nice thing is that it can fold in half, and has wheels to easily place it under your desk and remove it again.
The app is really crappy, and I wasn't able to connect it to my phone. But the pad itself does its job so I'm happy about it.
I mostly do 3.5 km/h, you can go faster than that, but then it becomes more difficult to really get work done.
