Comparison shopping for electronics requires learning the SST (Shipping and Sales Tax) dance. With very slim profit margins on most electronics, the biggest savings are often found in not paying hefty add-ons.
Sales tax is the easy one. Online and catalog retailers are only required to charge state sales tax for items delivered in states where they have a store, office or physical presence. This is bound to change someday, and some retailers are already voluntarily collecting additional taxes. And technically, some states require you to pay a "use tax" on items purchased out of state on your tax return. (Does anyone do this?) But for now, it remains a big savings opportunity. Many sites clearly identify where they charge tax. If they don’t, a quick check of their "about" or "contact us" page will usually let you know. Find a retailer outside of your home state, and you’re halfway home.
Shipping charges can be more complicated. Some sites require you to complete most of the transaction process before calculating these charges. Many sites use a "free shipping" come-on, but then scare you into paid shipping with (often fictitiously) long estimated delivery times.
Some comparison shopping sites offer good "best total price" calculators, which can be an easy way to find the best deal. Be sure to view all stores, and sort by total price; some comparison sites default to paid placements first. And the lowest total price isn’t always the best deal. Sometimes, it’s worth paying a few extra dollars to go with a known retailer, especially if they’re also part of a bonus shopping points program. The three I use most often are CNET, Pricegrabber, and Shopzilla.
Finally, don’t be seduced into buying extended warranties. Enroll in Buyer’s Advantage instead.