"I'm not cocky," Christina Aguilera explains in her new disco banger, "Vanity." "I just loooove myself, bitch!" Thanks for clearing that up, Xtina. Humility has never been this lady's problem — on her last album, the 2006 double disc Back to Basics, she was in way over her head aspiring to be a jazz singer, comparing herself to Billie Holiday and John Coltrane. But she's a lot more fun now that she's getting her Lady Gaga on instead. She goes for an electro makeover on Bionic, dressing in Gaga-style robot glam and cranking up the Auto-Tune.

Bionic has her friskiest synth beats since the days of "Genie in a Bottle," with surprisingly punk-minded collaborators like Le Tigre, Ladytron and M.I.A. "My Girls" is a hilarious disco anthem where Aguilera gives it up to her new riot-grrrl pals: "My girls wear lipstick while they're making my beats/They got guitar picks in their purses, Louboutin on their feet." Things stall mid-album with a string of dull ballads — "Sex for Breakfast" is cold cereal, and "Lift Me Up" is the inevitable Linda Perry snoozer. "I Am" is an intriguingly Björk-ish collabo with Australian folkie Sia. But "Vanity" says it all, especially when the backup chorus chants the wedding march as Christina vows, "I take myself to be my lawful-wedded bitch." Cheers to the happy couple.

“1999”

“I don’t consider myself a great poet,” Prince told Rolling Stone. “I just know I’m here to say what’s on my mind.” In the case of the apocalyptic party anthem “1999,” he was worried about then-president Ronald Reagan’s foreign policies. The song’s melody is based on a riff borrowed from the Mamas and Papas’ “Monday, Monday,” and Prince originally envisioned the first verse with three-part harmony but later split the vocals between himself and members of the Revolution. Because Warner Bros., with whom Prince was locked in a contractual battle, owned the original’s masters, Prince rerecorded the song and appropriately released that version in 1999.