What I found is that if a company has a problem and you sell yourself as the solution, you can ask for the moon. This highly depends on the company. If the company is simply looking for bodies, avoid :)

Even for the exact same job, I've seen pay difference of beyond 50% (even within the same team!). I helped this guy raise his salary from 85k(?) to 130k simply by showing him a piece of paper. (Don't ask)

Oh, another tip, discuss salary with your co-workers, only good can come out of it.