I finally found the Icterine Warbler here in Berlin! Just when I was beginning to believe that this bird is a mythical creature, I ran into two of them fighting in the trees on my way to get coffee this morning.
I was too non-caffeinated to know what I was hearing: my first thought was that a few nightingales decided to speak a different language today. This bird has a very wild song that cycles through an incredible variety of calls, trills, whistles and buzzes. At times it sounded as if an entire aviary was concentrated into one point in the tree. After staring in frustration at a bunch of trees and nearly twisting my ankle on the curb while trying to follow the sound, I decided it would be safer for everyone if I went on to my coffee. Happily this guy was still singing and yelling and jumping around all over the place when I returned, and with my sharpened senses and quickened reflexes I was able to capture a few shots of him. His friend/enemy had flown off to a nearby tree, but was singing just as madly in the distance.
You can see a video of him here. (Unfortunately he really wanted to show me his butt for the video, sorry.)
Thanks Steve for letting me know about this bird!