Pre-paid German SIM card for visitors? (Cologne)

Hi all. I am planning to visit Germany for a week and was wondering if they sell pre-paid SIM cards (calls, texts and data) for visitors. I heard that I'd have to provide a local address in Germany to get one, but can I give my host's address?

If this is not possible, can I get a 3G data SIM card from a mobile shop which allows me to connect to the Internet with a USB dongle? Which company would you recommend? Thank you. :)