Broadly counted every instance of rape, murder, and nudity in "Game of Thrones." An introduction to this data and methodology can be read here, along with the total numbers across all seasons.
Notable deaths: Robb, Talisa, Catelyn, Ros
Notable rape scenes: Brienne's attempted rape, which Jaime stops (and loses his hand for intervening in)
Despite featuring the notorious "Red Wedding" episode, this season saw the lowest number of onscreen deaths. Unlike the first two seasons, however, this is the first season to show more than one woman's onscreen death.
This season, the first woman's death we see is Ros, a smart and kind prostitute we've followed all the way from Season 1 in Winterfell to King's Landing. We see her tied up to a bedpost, nipples exposed, impaled repeatedly with arrows from the boyking's crossbow. Apart from Robert Baratheon's infant bastard daughter who was brutally murdered in a brothel, Ros is the second woman whose displayed corpse is meant to traumatize the viewer (the first is Sansa's Septa, whose decapitated head was put on a spike outside of King's Landing), marking a trend of women's deaths being used to indicate extremely evil acts.
Other notably brutal, gendered deaths occurred at the Red Wedding: Walder Frey's teen bride has her throat slit by Catelyn Stark, who then meets the same fate. Robb's wife Talisa is repeatedly stabbed in her pregnant belly and shown bleeding out.
Season 3 also made me suspect that writers Benioff and Weiss like to prove someone's virtuosity through their sexual skill. In "Kissed by Fire," the virgin Jon Snow apparently reinvents oral sex in a cave with Ygritte. In "Walk of Punishment," the bumbling squire Podrick is revealed as a great lover with a possibly enormous penis, even though we're already endeared to him for saving Tyrion's life at the Battle of the Blackwater.