Here is a great website I have come across :- http://www.melodycatcher.com. - I have just added this to my favourites. Do you have a melody stuck in your head, you can't think what it is but you know how it goes?  The MelodyCatcher is a music search engine in which you can enter a melody or musical line via a simple keyboard-like Java applet interface. The melody is then searched in their database and the closest matches, if any, are returned. Each search result is presented with a link to the original audio file along with its source on the Internet, and a play button for instant playback. Although songs can also be searched using text, what makes the MelodyCatcher different from conventional search engines is that it is not limited to just text. The MelodyCatcher can be highly useful to those searching for songs for which little or no textual data are available, e.g., the song is an instrumental, or the user does not remember the artist, title, or any lyrics samples.

Their site shows some hints for entering the melody:-

    * The rhythm is ignored in the search engine. When you enter the melody on the keyboard, you can do that note by note.
    * You do not need to enter the full melody: the first 5-7 notes will usually be sufficient to identify a melody.
    * the key of the melody is not important; you can start with any note you choose as long as the replayed melody sounds similar to the wanted melody.

Although song titles can also be searched using text, the Melody Catcher is especially useful to make accessible the on-line MIDI world by melody input. In many cases, the system can also be of help to find and compare more or less similar MIDIs.

For more information, visit their web site at http://www.melodycatcher.com/.

I have received a comment from J L van OS in the Netherlands who has added that :- "Of any played theme all notes are described as text in the field called  "Notes”.  With the commands Ctrl-C  and Ctrl-V these notes can be copied and pasted.  This text can be used for instance to mail this  theme to a friend who then can use the same commands in the Melodycatcher to listen to it".