1. The Fifth Doctor Saving Peri At The Cost of His Own Life (The Caves of Androzani, 1984)
This episode has been growing in stature during the last few years, and thats no surprise. Its got everything someone could want in Doctor Who including a regeneration as the Fifth Doctor goes away (with the Master taunting him), and the Sixth Doctor comes along. That it happened because the Doctor chose to sacrifice himself to save Peri makes it all the more bittersweet.