A new google like type search engine for music files has emerged, http://skreemr.com/advanced_search.jsp (the advanced search page), you can here search for music and the service will then scour the Internet for the MP3 you seek and return a list of possible links.  Once you click a link the music is ‘streamed’ to your computer (right click on the link and save link as will allow you to ‘download’ the music).

It also has a custom software which can be downloaded here;
http://songr.co.cc/

Legality;
Some in Denmark claim that this is not ‘true’ streaming as the file is downloaded before or during playback and that you thus is breaking the copyright.  I don’t know, it’s a gray zone so you need to consider both the legality in your country and your continence also…  never the less an interesting search option.