vogelstimmen.de
You only need part of the bird's name to search for it. The keyword must consist of at least three letters, anything less will result in an empty page.
A maximum of 20 search results will appear. You can listen to them, email them, or use them to start a new search.
The birdsongs are available online in different formats. In order to listen to them, you will need the appropriate software and browser plug-ins. I recommend Winamp Media Player and the VLC Media Player, both of which can be downloaded for free.