And to point out something slightly obvious, if you're looking for an easy start on the original run, BBC America is running one story per Doctor each month this year, as detailed in another thread here.
http://www.trekbbs.com/showthread.php?t=200980
Next up is Tomb of the Cybermen, an interesting story for two reasons: until 1992 it was missing, and was something of a holy grail for missing episode hunters; and more recently, Matt Smith watched it between getting the role and starting recording, loved it, and by all accounts let it have a major influence on his performance (and certainly his costume)...