Costco automatically doubles the manufacturer's warranty (and some credit card companies also do it too, if paid using the card). Costco has local warehouse locations (and an online website) - same for Sam's Club [owned by Walmart].
Lowest retail prices (day to day) are at Fry's Electronics [but locations are mainly limited to California and Texas].
Other retailers with either low prices, or special discount sales (and/or coupons), are Best Buy, Circuit City, Target, Sears, CompUSA, K-Mart etc. Many of these will price match another store's current non-closeout price (but usually not any online price, except their own site's price).
The best sale of the year is coming next month - BLACK FRIDAY (day after Thanksgiving), especially early Friday discounts, many available only for walk-in customers that morning. You should pick up the Thanksgiving day newspaper for the many advertisements from retailers, to give you an idea of the sale prices to expect.