My first steps into amateur radio, and I suspect for many others, were preceded by listening to medium and shortwave broadcast stations on home made crystal sets and later on my first ex-WW2 communications receiver. There was a real thrill in hearing the once familiar tunes that proceded broadcasts on the hour or half hour from distant stations around Europe or much further afield. I recall, for example, the sound of the kookaburra bird from Radio Australia fading in and out of QSB in the early morning before breakfast time. Also the familiar sounds of Radio Moscow and the other eastern block stations. Most of these are now long gone but there are websites where these old interval signals as they are called, and much more recent ones, are available to hear.
One of the best is http://www.intervalsignals.net/ where a huge collection is available to listen to as MP3 files, but not to save.
See also http://www.youtube.com/watch?v=hFRYKDF2kxs where a smaller collection is available and can of course be downloaded and saved (see left).
Another site http://garlinger.com/QSL/qsl.html has a number of QSL cards which link to the interval signals of the stations shown.