Yes, there are free downloads on the internet, and yes, there is music that is "legal" for you to use - it is in the public domain, or the artist has licensed it with a Creative Commons license that allows other to use their work.
C/Net music.download.com You don't have to create an account. There are over 100,000 songs to download. There are many ways to sort the songs--song name, artist name, average rating, total listens, total listens last week, date added and date updated.
On Jamendo artists allow anyone to download and share their music. It's free, legal and unlimited. You will have to register for an account, and an email will be sent to you to confirm your registration. It's very easy to search using a tag cloud. Here's a widget from Jamendo playing the album Suerte by Pastèque (This album is released under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.5 Generic License)
The FreeSound Project might be a useful source of sound for you project: "The Freesound Project is a collaborative database of Creative Commons licensed sounds. Freesound focusses only on sound, not songs. This is what sets freesound apart from other splendid libraries like ccMixter. New to this site? Read the What is Freesound page to learn more!" Registration required.
I foud a really neat HeartBeat sound on this page:
Oddio Overplay offers music in a very easy to use layout.
Enter the kind of music you want to find in the search bar; you are taken to a page of results. To download music, right clicking the link and choosing the SAVE option works with both Apple and PC systems. In some systems, left clicking prompts a dialogue allowing the user to choose to either open (play) or save (download) the file.
"The primary purpose of this site is to connect artists and audiences. Artists who want the world to hear their music offer it online for free. This music is completely legal for a listener to download and enjoy. Oddio also refers visitors to music archives, such as the United States Library of Congress, Opsound, free netlabels and the Internet Archive, that are using the Internet to allow the public to access their sound resources."
Soundsnap Soundsnap is a free online sound library and community for sound designers and producers. People can upload sounds and share them with the world.All the sound effects at Soundsnap are uploaded by creators. There are many thousands of audio clips already available. You can search for sounds via the search bar at the top, browse by category or browse by tag. On the sound 'teaser' click on the upper right corner an choose between mp3, wav or aif to download.
The Red Ferret site lists "1 Million Free and Legal Music Tracks" through a very long link list to portals, review sites, specialist sites, general music sites, record labels, non-English music sites, and bands offering mp3s.