eClassical.com has six free mp3 tracks which change most days.
Five are at the link provided, the other is on the site's home page.
They also have complete works of popular classics eg Mozart symphonies, Beethoven Symphonies for US$0.99. They have suggestions for music for different occasions (eg weddings), and special offers of US$5.99 for around 100 minutes of music.
A great way to get acquainted with classical music. It's all completely legal and they even have a money-back guarantee if you don't like what you have downloaded!
Thanks!
There is another free song at the bottom of the homepage