[ryandrake]

If your company is public, you can take a crack at that one using public data.

    My current company's Operating income (EBIT): $X
    My current company's Labor cost: $Y
    Number of employees: Z

So, on average employees at my company are worth ($X+$Y)/Z. Then you start adjusting. I'm a knowledge worker, so my contribution towards EBIT is greater than average (say, by 20%), etc. You can probably come up with an objective measure of your "worth" that is far more than you are making. That's what you start the negotiation with.