Free and cheap WiFi in Berlin

It has been more than a month since I got back from Berlin, so I need to backup my memory of hot spots in there:
Wifi is actually pretty expansive in Berlin - there are many hot spots, but to surf you need to either pay directly to an ISP, or use your own account (assuming you have one).
Here are the few locations I found:

• Cheap connection in the Häagen-Dazs cafe in Kurfürstendamm street
• Free access in Europa center
• Tegel airport