[1] sums it up, the essence is that they know better than you what they can afford and that by offering a number you only disadvantage yourself. If you're uncomfortable about negotiating an optimal package just make them make you an offer and if it exceeds a threshold take it...
Also, apply to several other jobs so you have competing offers. Do mention your other applications if specifically asked. And in end-stage negotiations feel free to play the companies off each other, such as "Sorry, I'd really love to accept, but I have a competing offer that makes much more financial sense for me at this point. I haven't firmly accepted the other offer yet, as it's been a very difficult decision since your company has such a wonderful opportunity." But don't bluff and don't act like you're taking a bank hostage; be civil, honest, and prepared to follow through on what you say. And at this point, Joel's advice applies: http://www.joelonsoftware.com/items/2008/11/26.html
But at the end of the day don't get too wrapped up in money or extracting maximum value. You have years and years to climb the pay ladder.
If you need a job because you are unemployed or something, well, that's a different situation entirely.
In addition to salary, also consider equity, which is a different discussion depending on the size and stage of the company.
Piaw Na's book has a good chapter on compensation negotiation regardless of your geographic area. It's well worth the $25: http://books.piaw.net/guide/index.html
See also iaw's advice. Good luck!