Amazon.com
Great place to shop whether your looking for the latest accounting text book or a case of snacks in their new grocery store. Definitely visit their Friday Sale which is on their 'Todays Deals' page. Here you'll find some great deals (which techbargains.com often highlights too).
In a rush to get a piece of gear for the office...you generally can't lose if you buy from newegg. The prices are great. The service is great...they process orders very quickly. Their on-line store is one of the best I've used. Just be aware that a lot of their products are OEM and don't come with retail packaging. For the price, you can't go wrong.
Check for on-line coupons!
When shopping on-line, finding a deal is simple. One of the easiest things you can do is check for on-line coupon codes. If the merchant you are buying from has a box in the checkout process for a coupon or discount or promotional code, don't ignore it. There are websites out there dedicated to tracking on-line store coupon codes. One particular site I like to use is XPBargains: http://www.xpbargains.com/.
Buy.com is another site with generally great prices. You can usually find a coupon code to make the pricing even better. This Christmas they had some great deals and a $20 off $50 purchase with Google Checkout. Wide variety of products makes it a one-stop shop (where Newegg was solely computer products).