If you're not content to pick up Gran Turismo 5 Prologue in stores on a fancy Blu-ray disc, Sony has uploaded the game on their shiny new PlayStation Network store. The download will set your hard drive back at least 1.9 GB and your wallet $40 (same price as retail).
While not initially available on the PSN version, you can download the intro and ending films at your leisure to view (the latter unlocked only after beating the game, natch). However, a documentary on the series, "Beyond the Apex," appears to be exclusive to the Blu-ray version for the moment.