It's sometimes forgotten that most of the greatest composers in classical music were also superb improvisers. Bach amazed audiences with his improvisational keyboard skills, Beethoven was always game for an improvisational showdown with other musicians and, by all accounts, Liszt drove women crazy with his flights of romantic fancy during performances. No wonder, then, that the history of jazz is peppered with "jazzed up" versions of classical compositions. Here are five of them. By all means, add your favorites to the list.