The following represents my suggestion of what order to watch episodes of the new Doctor Who and its spin-offs, Torchwood and The Sarah Jane Adventures, to keep the events of each show roughly synchronized for the sake of their occasional crossovers. (Note: The Sarah Jane Adventures ended at episode 5.6 and Torchwood is currently on indefinite hiatus.) This version is current through the end of 2012.
This list includes seven classic (1963-1989) Doctor Who serials that I think help maximize one’s enjoyment of the newer franchise. An explanation of these choices can be found here, although that link includes spoilers. If you do not wish to view any of the older series, you can skip down to the episode “Rose,” which was the first of the “New Who” franchise: