Being in the hotel industry, I can tell you that all of the major sites (Expedia, Travelocity, etc.) are just giant advertising sites. The more money the hotels pay them, the higher their hotels gets put on the page. You are not necessarily going to get the best rates on any of those sites.
What I recommend you do is look at Trip Advisor and find a hotel that appears to be in your price range and that gets good reviews. Then see what they are charging on their own website as well as Expedia, Travelocity, Hotels.com, etc. Now you have an idea of their rates. Call them directly and see if you can get a little bit better rate. Try calling the hotel directly, NOT the toll free reservation line. If they are charging $100 on Expedia, they are only going to get about $80 of that money for the room. The remaining 10-20% will go to Expedia for a commission, as well as a few bucks for different website processing fees. So offer them $85 if you book directly instead of going thru a website. Odds are they will accept the offer. They will make more money and you will pay less. Essentially you are cutting out the middle man.
I recommend you call in the middle of the day. The general manager will usually be on duty and can approve rate requests. If you call during check in or check out times when the front desk is busy, you might not have as much luck negotiating a rate.
Sometimes you can also get a 1-2% discount by paying cash. You can guarantee with a credit card, but then agree to pay cash when you arrive. This saves the hotel 1-3% on credit card processing fees.
Also, if you are staying multiple days, ask if it's possible to get a discount and only have housekeeping every other day if you don't mind making your own bed.
In addition, ask if they have any less desirable rooms for a cheaper rate(ie, parking lot views, etc). I've also been able to get discounts by agreeing to let them charge my credit card in advance and agree that it is non-refundable (but only if I know for sure that I will go).