Which WiFi USB Dongle for Pi2?

After moving my pi2 to a room without ethernet access I want to add a WiFi USB Dongle. I tried search but seem to fail to find one that should work effortlessly (instalation wise, I am aware of WiFi limitations). I found a thread suggesting virgin branded WNDA3200 adapters (which use ath9k (must admit I do not know what that is) but can't seem to find those now. Any recommendations for a dongle on ebay or aliexpress?