The earliest telling of the story of Apollo and Python is in the Homeric Hymn to Pythian Apollo (scroll down to lines 277 to 374). Ovid's re-telling of the story comes after his version of the flood.
This story seems to have inspired artists of the 19th century in particular. The Tate Gallery has an example by Turner (1811) while the Apollo Gallery in the Louvre has a ceiling by Delacroix showing Apollo slaying the Python (click on the picture to see a larger version). The picture was commissioned in 1850 when the gallery was being restored and painted from 1850 to 1851. The Louvre's site also has a short video of the gallery, which I haven't actually seen as you need Quick Time to view it. The National Gallery of Canada has Gustave Moreau's treatment of the subject from the early 1880s.
Once again we can bring you a modern video production of the story.
