As a feminist, I am a serious supporter of hearty negotiating. It may be because I am a Jew from the Northeast and my father was a salesman, but I have no problem talking about money. I do have some trouble asking for way more money than anyone else, so I don't tend to do that. I am more likely to find out the salaries of current faculty and to define for myself what seems reasonable--on the high end of reasonable, of course. As Dean Dad said, where you start dictates your income for years to come, if you stay at the same school.
At public schools, you can find out the salaries of current faculty members by asking the reference librarian for the list of salaries. They are called different things at different schools: university budgets, salary books, etc. (At private schools, I believe that you need a little inside help or you have to rely on aggregate data in the Chronicle. I am a public school kinda girl, so that is what I know firsthand.) The public school salary data are housed in different places at different institutions--libraries, faculty senate offices, and institutional research offices. The reference librarian always knows where they are.
Sometimes I find the salary data as part of my campus visit (called "visiting libraries") and other times I find it on my own--at the end of the day or when I first arrive. For one job interview, I knew I would have no time on campus to do my research, and I thought it was possible that I would get an offer on the spot. So, I called the reference librarian at the school before I went, and I got her to give me the info over the phone. That kind of service is rare, but I think I bugged the librarian so much that she did it basically to get me off the phone.
Dean Dad notes the particularities of schools with unions, and I have never actually worked anywhere that had a union, though I have friends who do. Deans at union schools are limited by the union contracts as regards actual salaries, but there are any number of resources that Deans usually control that can be negotiated. These resources include: start-up research money, TA and RA support, summer pay, moving expenses, timing of the beginning of pay, office furniture and computer technology, support for conferences and research travel, and so on. Everyone should include some if not all of these resources of the job in their negotiations.
There is a piece of negotiating that is an art. The candidate (you) has to be friendly and forceful at the same time. You want to drag it out long enough to make them deal with you, but not so long that everyone on the faculty and administration sees you as a diva (male or female, though women seem more likely to get tagged as "difficult" or "arrogant"). You want to be thorough (addressing those resources I mentioned) and yet not exhausting or unreasonable ("I must have the Levenger cherry wood desk"). The best negotiators approach the negotiation as just a normal stage of the hiring process.
Remember that the Dean's job is to get you as cheaply as possible without completely insulting you or losing you to another school. Deans will often talk with you about salary equity and his/her need to keep your salary in line with folks who have been on faculty for years. Don't get too taken in by that line of argument. It does not benefit other folks if you are paid poorly. In fact, if you get paid more than they do, most institutions eventually deal with the salary compression and wind up raising salaries to address equity issues. So, really, you help them more in the long run if you get paid what the market can bear (within reason).
Your job is to get as much as you can without being petty or unreasonable. If you are coming in as a brand new assistant professor, it is unlikely that you will be offered more than a full professor. However, you can easily make as much as or more than the other untenured professors. And, as for those additional resources--if you don't ask for it, you definitely won't get it. If you do ask, and the request is basically reasonable, the worst answer you can get is 'no.' It is extremely unlikely that a Dean will withdraw the job offer because you asked for something; more likely, they will just tell you that they can't do it. Of course, if you ask for something completely insane (and we have all heard of those), you will become the topic of much discussion and speculation for years to come. So, keep your requests reasonable, related to your rank and institution. (An aside: I am always amazed at some of the resources allocated to those higher up the food chain. It actually helps me negotiate. If a President gets country club memberships, a job for the spouse, a car, and a bonus for not leaving, why not ask for a little summer money?)
I have found that negotiation has gotten easier as I moved along in my academic career. I have more of a track record, a better sense of reasonable salaries/resources in my discipline, and an idea of what I really want and/or need in a job. That is not to say it is always easy for me. During my second job search, I had one negotiation with a Dean who sought to make me feel guilty in every conversation. While I held my ground on the phone, I literally cried after every phone call. Ultimately, the job offer did not work out due to a state hiring freeze, and I must say that I probably was lucky that it didn't. I can't imagine dealing with that Dean for years.
As an administrator/faculty member, there are a few extras to factor in. First, it was important to me, based on some great advice I got from other administrator friends, that I get at least a 10-month contract, but not a regular 12-month contract. The difference is important: a 10-month contract means I will need to be around a little in the summer, and my time attending meetings and working in the summer is paid, but I still basically have a faculty position. A 12-month contract means I have to act more like staff--at the office everyday, during regular office hours, and probably fairly well-dressed. (Okay, I admit it... I really like faculty life. I want to come in late, dress more casually, and work at home if it suits me. I have been surprised at how easily I have moved into spending more time in my office, but I fool myself into thinking that it is really optional.)
I have also learned that there are additional things I should have negotiated: support student/staff, funds for administrative training (separate from research monies, since I am still expected to do research), an office appropriate for meetings with students/faculty/staff/potential students and their families, a guarantee that I would qualify for a sabbatical like other faculty members, and travel to administrative/leadership conferences. Some of these I have had to negotiate post-hire, and others have yet to be negotiated. Hopefully, I will take what I have learned into my next negotiation.
I also hope that we will all take what we have learned and share it with doctoral students and colleagues. When we talk with doc students about job hunting, I am the one who focuses on the negotiation process. I want students to practice negotiating. I want the Dean to explain what it is like from his or her side, and what s/he thinks when s/he is negotiating with a candidate. I want there to be workshops on negotiation at our national disciplinary conferences. The better we are at negotiating up front, the more we raise the salaries in our discipline, the better off we all are in the long run.