Magic Lantern: a Step by Step Install Guide
Dave Dugdale gives a short video which will guide you through the process of downloading and installing Magic Lantern 2.3 (current stable version) – the alternative firmware for canon cameras (Dugdale uses it on T3i/600D).
Magic Lantern is an open source software (actually firmware although some simply calls it a hack) for Canon DSLR cameras. It does not delete the existing original Canon firmware but instead runs alongside it from the memory card (so if you remove it you will get back to your original firmware).
Magic Lantern 2.3 is a very powerful tool which lets you add many different functions to your existing Canon camera – you can see some of them in the following video and read about them on the Magic Lantern site.