They will usually match any online rate you can find. This past weekend I needed a last minute room in a majorly busy town, found a rate on priceline (not name your own, but where they give you an exact price), called the hotel direct (not the 800 number), and a manager overrode the price to give me the match. It was HALF the rate that the room was going through on their website! He didn't sound too happy, but didn't ask me to email or fax him a copy of proof, so he's an okay guy in my book. It also helps to be a member of their "club".
Good luck!
Terri