From other SF shows...
Mira Furlan (B5, Lost)...I know, I know, but there's something about her voice...
Starbuck, Boomer, Caprica, Deanna, Admiral Cain, Admiral Cain's CAG in Razor, Cat...in fact all the ladies in BSG 'cept Laura. She has that weird permanent semi-smile on her lips and I just can't get past that.
Can't believe no-one's given mention to Sarah Conner - goes from fluffy waitress to Terminator, yet still retains her femininity (which is ultimately what saves her from becoming the thing she fears and hates the most...)
I'm also with whoever nominated Lyta Alexander. Interesting factoid about the actress who plays her - before she started getting parts, she was a stuntwoman, which is pretty empowered by anyone's standards...