Just Google the item you're looking for. You'll find a number of "comparative" sites to check prices. Each vendor is also assigned a rating earned by customer feedback to the comparative site. That way, you can see who's trusted by consumers.
As an example, I just bought an Arctic Cooling Freezer7 from a site I hadn't heard of before. The total price (incl. shipping) was the same as Newegg's w/o shipping.