Is there a site to find the lowest price for something?

Looking for A Canon Rebel T3, Nikon D3100 and a few other cameras. I'm seriously wanting to buy now, but if they go on sale cheaper then I will wait. I know I can't SEE the FUTURE deals, but I want to know the past deals. There's a camera for $698, but if it has been on sale for $499 or $550, etc. Then I will wait to see it on sale for a price close to the previous sale.

I don't know of any good vendor that sells those cameras at less than retail. Some P&S cameras may go on sale when they are replaced with a newer model.