I'm reminded of a study I read a looong time back (sorry I don't remember where) that looked at how in situations where there is a shared armrest (think movie theatre or airplane) between two strangers, the men tended to be the ones who end up using it more. That wasn't malice, it was just an unthinking gesture. Ever since then, I've been hyper-aware of seat armrests. :-)
I think one takeaway from this is to be aware of the dynamics in your daily conversations and just watch. Pay attention to what's going on. If a man and a woman talk over each other, cast your eyes to the woman instead of the man if you think she has something interesting to say. Subtle things like this can make a big difference. If you do this in the office, the feel like you value them more and you will find yourself with new allies.
I would also suggest that if enough women ignored the stigma associated with being labeled a bitch, they would move the line is drawn a bit. That's not always possible but again, being aware of it helps.