Jessica Simpson

This song too has a disco beat so fierce it’s practically macho. And it starts with a knowing tease as Beyoncé summons the instruments one by one: “High-hat. 808. Jay.” (Drums, a drum machine and a rapper boyfriend: what else do you need?)

But the refrain doesn’t give Beyoncé a chance really to show off, and Jay-Z’s second verse in particular sounds a bit clunky. It’s a fair-to-middling single from a singer who is the opposite of desperate: Beyoncé has already topped the charts this year with her keyed-up Slim Thug collaboration, “Check On It.” One way or another, she’ll do it again.

Listeners in search of the next “Crazy in Love” should be looking instead to Ms. Aguilera, the unpredictable former teen-pop star. Her 2002 album, “Stripped,” included a garish club track (”Dirrty”), an inspirational ballad (”Beautiful,” accompanied by a pro-gay video) and a feminist hip-hop collaboration (”Can’t Hold Us Down,” featuring Lil’ Kim).

Ms. Aguilera’s new single, “Ain’t No Other Man” (RCA), comes from her forthcoming double-album, “Back to Basics.” It’s devastating: all hard drums and horn blasts, with Ms. Aguilera delivering a series of nimble vocal runs and roaring ad-libs. (The song was produced by the pioneering hip-hop producer DJ Premier.) The period-piece video, directed by Bryan Barber, casts Ms. Aguilera as Baby Jane, a jazz singer tearing up a Harlem speakeasy. And for now her only problem is a happy one: How on earth will she top this?

Ms. Simpson, on the other hand, is a hugely successful singer with nothing in particular to top. Her 2003 album, “In This Skin,” sold almost three million copies, and yet it’s hard to think of a Jessica Simpson song everyone knows. What everyone knows of course is that her marriage to Nick Lachey was chronicled on a reality show, “Newlyweds,” and that its demise has been chronicled in the tabloids.