That's cool, man - the question just read a bit weird to me; likewise, it wasn't my intent to come off sounding aggressive. Tone doesn't always translate well online - I need to use more smileys.
FWIW, I'd say your guy friends are missing out on a lot of ass-kickingly great bands.
The Corrs are good; if you like them you'd probably really like The Cranberries. Enya is always great (as is her family band, Clannad).
Some more good female singers/bands in my collection I'd put forward who are in the heavier/alt/not pop category:
Jack Off Jill (who later spun off into Scarling)
Tura Santana and Manhole, who were both earlier bands of the vocalist for My Ruin
Kittie
Straight Line Stitch
Porcelain and the Tramps
Ego Likeness
Infected Rain
Animal Alpha
B*tch Alert
Betty Blowtorch
Madder Mortem
Switchblade Symphony
The Horrorpops
Zombie Girl
Lacuna Coil
Stolen Babies
Walls of Jericho, Exilia, iwrestledabearonce, Cadaveria and The Agonist are also very heavy, though I don't favor them personally. There's Emilie Autumn, Tribe 8, The Lunachicks, Le Tigre, Ayria, Halestorm, Flyleaf, The Butcher Babies, In this Moment, Huntress, K's Choice, The Dresden Dolls, The Sneaker Pimps...
And Gin Wigmore is absolutely fantastic.
I... listen to a lot of female artists, in case that wasn't abundantly clear by this stage.
