I just accepted an offer for a job.

speaking with several people who have that same job I have been told the offer I accepted is 25-40K below market value. Is it too late to go back to HR and ask for an increase after I have already formally accepted the offer? I was not able to find any real comparables online because the numbers on payscale.com and salary.com and valt are inacurrate. If it is too late do you think it is a good idea to get them to match my salary to a competing company within a year?

I want to make some potential friends specially from the South as I intend re-locating Are their any sites that are not like 'meat markets' online