Not only are sisters doing it for themselves, but lately in pop music, they’re pushing the boys off to the side. While once-hot male stars like Usher, Chris Brown and 50 Cent struggle to inch into the Top 40 on Billboard’s Hot 100, Lady Gaga, Beyonce, Rihanna, Katy Perry and Taylor Swift swing, hit and score with single after single.

In song, they don’t even need the comfort of a man anymore. Lady Gaga flaunts her bisexuality in her signature hit “Poker Face,” a woman makes a confession (I love you!) to Rihanna on the dance floor in the Rated R track “Te Amo,” and in one of the biggest singles of the last two years, Katy Perry kisses a girl — and she likes it. Where’s Justin Timberlake when you need him?

Album sales are on the girls’ side, too. The two best-selling long players of 2009 were both by women: Taylor Swift’s Fearless came out on top, with 3.2 million units sold, while Susan Boyle’s I Dreamed A Dream moved 3.1 million in the final weeks of the decade to become the year’s second-biggest seller.

But it was the Boyle album that emerged as the Avatar of music at the end of 2009. For several weeks there, the tops of the pops on the Billboard 200 album chart felt like the summer box office, only instead of being dominated by testosterone-fueled blockbusters, the headliners were all packing estrogen. The only two serious threats to Boyle’s chart supremacy, Alicia Keys and Mary J. Blige, also outsold every guy in sight.

In the end, Boyle was knocked off her perch last week by — you guessed it — a woman, a newcomer who goes by the name Ke$ha. The boys may be back on top this week, as Vampire Weekend ascends to No. 1 with their second album, Contra, but they’d better enjoy it while it lasts. Boyle’s January 19 sit-down interview with the queen of all power women, Oprah Winfrey, all but guarantees her a quick return trip to the top.

Meanwhile, the most eagerly anticipated album of the new decade? Soldier of Love, a 10-years-in-the-making opus by a very famous lady: Sade. The warrior reference is fitting. Though male-dominated Oscar-season war films like The Hurt Locker, The Messenger and Brothers paint a different picture, in music, the girls are just as fighting fit as the guys.

In the video for her current Top 10 single, “Hard,” Rihanna wields a machine gun, runs around in haute battle couture, catwalks across an exploding desert, and proclaims herself “the hottest bitch in heels right here.” Lady Gaga already offed her lover with a dose of poison in her “Paparazzi” clip, and everyone who saw her MTV Video Music Awards performance last September knows she’s not afraid to get a little bloody. Now we’ve got Sade, pop’s empress of cool, ready to don her fatigues and fight — for love and continued chart dominance in pop’s battle of the sexes.

May the best women win.