Check out...
PJ Harvey's early stuff (Rid of Me, 4-Track Demos)
The Breeders
The Amps
Elastica (especially their album The Menace)
Le Tigre (especially their first album, self-titled)
Bikini Kill (though some of their stuff is a little too angry, their last album Reject All American is awesome)
Bratmobile (if you like lo-fi punk with a bit of a surf guitar influence)
There's also a woman named Marnie Stern who's supposed to be a hard-core shredder on a guitar, but I haven't bought her stuff yet.
And three female artists I've been digging a lot lately are Annie, The Blow, and MIA. None of these are rockers really, but each does something that's definitely not singer-songwriter stuff. Annie is kind of like traditional dance pop (in the tradition of Madonna) except that it's really really good (and really well produced); The Blow is similar to Annie except a little more lo-fi and the electronic beats are more experimental; and M.I.A., if you don't know her already, is a Sri Lankian hip hopper who mixes elements of world music to create a bumpin' pastiche. She's also got a great voice.