Suzanne posted a link to Economic Woman's post on salary negotiation in response to my post on the same topic, and I think it raises some important points. It's well known that women make less than men. The most popular statistic fails to account for profession, education, hours worked, and experience. However, even studies that control for this show some gap. One hypothesis is that women are less successful than men at salary negotiation. Note the words less successful, not bad at. It may be that women don't ask because they don't care (I find this unlikely). It may be that they do ask, but aren't as skilled at it for reasons that are their own fault. It may be that they ask, but their bosses react differently than they would to a man, and so the woman is less successful, or even penalized for doing so. Men may face the same risks in asking for a raise, but have a higher risk tolerance, either due to innate preferences or because women are more sensitive to wage fluctuations (maybe because they're more likely to head single parent households). And for all these reasons and more, women may draw the perfectly rational conclusion that they're better off not asking. I have not studied the research on this in any detail, but none of the news reports I read indicate that the studies done are capable of discriminating between these hypothesises.
So what can you do? I wish I had better answers. I've already talked about how negotiating with managers makes me fearful and uncomfortable, so I'm not exactly a role model. Beyond my advice for general negotiation, I would say:
1. know this research, because knowing is half the battle.
2. be in an in-demand field. Being discriminated against by 90% of employers in a field with 1000 jobs is a lot more fun than being discriminated against by 90% of employers in a field with 10 jobs. Even if that last guy isn't prejudiced, and you somehow land that job, and he pays you market wage, you have no credible threat of exit, because you know, even if he doesn't, that nothing else will pay you as much as he does, and that will sap your will to negotiate for even more. As a bonus, in-demand fields (like software engineering) tend to feature substantially less prejudice, because driving away talent hurts corporations in a way it does not hurt restaurants or even university chemistry departments, where the supply of good candidates far exceeds the demand. Alas, this advice is unuseful to anyone without the talent in and enjoyment of such fields.
3. find a hack that lessens your fear. My hack is using third party agencies: I fear no loss of precious, precious goodwill, since the few ways they have to hurt me (like screwing up my paycheck) will hurt them and are legal actionable in a way that giving me destined-to-fail projects is not. Plus, they can't stand at the coffee pot and glare at me. And they're so brazen in their attempts to push my salary down that I can't possibly feel guilt about fighting back. It would be like feeling bad about filing a police report after you were mugged.
Anyone who's found a useful hack is encouraged to post it here.