Stick to the on-line sites that are real stores not just internet businesses. Amoung the best that are authorized resellers of all their equipment are J&r Music, B&H Photo, Crutchfield, and Onecall to name 4. These sites offer products from the large manufacturers such as JVC, Sony, Yamaha, etc... at great prices because their overhead is much lower than Brick & Mortar stores. If you are after something more high-end such as Creek, Adcom, or Parasound then checkout Audio Advisers.
I have bought from all these stores without a single problem.
Happy Hunting