God, I love "A Good Man Goes to War." The first time I saw it, I was kicking my legs out, Moffat got me so good.
Also, bookmark this video and watch it after you've finished Series Six and you've seen River's first (to the Doctor and the audience) appearance in "Silence in the Library"/"Forest of the Dead." River herself explains the chronology of her whole life on "Doctor Who Confidential," a late, lamented companion series that was like televised DVD bonus features after EVERY EPISODE.