Ah, so many possibilities! I wish I could have sound clips of every band up here, but realistically, it's not going to happen, for many many reasons.... So supposing your record-buying budget is not unlimited, what should you try first? Here is a very biased list of recommendations to start you off.

Acrid
Ferocious. Stupendous. I don't even know what the girl does in this band but they're so great I don't care. Grindy and lurching and blindingly intense.

Garmarna
Maybe not technically metal, but still heavy, and scarier than King Diamond. Gory medieval Swedish ballads sung and played as befits their gruesomeness.

the Gits
Seattle heavy rawk band circa 1992 - heaven only knows how the Gits avoided a lucrative record contract, international superstardom and a big ol Grunge tattoo on their collective forehead. It's a damn shame nobody knows about them, cos their song "Second Skin" might be the best rock song ever.

the Haggard
Tremendous two-woman Portland band - Emily on guitar, sts on drums, and they both growl/howl/scream. Punk Rawk and fan tastic.

Initial State
Grindcore with a social conscience and duelling female-male vocals. Just recently reissued, so you should be able to find it in your better record stores.

Melt-Banana
Inspired lunacy shouted/barked by YaSuKo and played by the tightest band in the history of the world. Is it grindcore? Is it punk? It's freakin genius, dood!

Romantic Gorilla
More inspired lunacy (sample lyrics: "I gorillaman! My dream is growing long long hair!") sung in an acrobatic scream-growl - kinda hardcore, kinda metal....

Walls of Jericho
Andy: "best female hardcore vocals ever," and if you ask me, Candace Kucsulain is in the running for best hardcore vocals, period. Slayeresque guitar, bloody-throat singing - intense metalcore.

Yellow Machinegun
Rapidfire catchy hardcore-metal songs about french toast, growing a tail, conservation.... The coolest band ever to share a bill with Limp Bizkit.