here is some basic negotiation advice http://jobhacks.wordpress.com/2007/08/08/offer-negotiation-t...
regarding the comment to mention another offer, that is cool if you really have one. It wasn't clear if the poster was recommending a "bluff" which is not a good idea at all. More important than the offer is how will the experience increase your value in the market. http://jobhacks.wordpress.com/2007/08/01/career-equity/