www.staples.com - A mixed bag. They've always got great coupons that can get you as much as 100% off stuff you buy (no, really), but their order system needs serious work. Several times I placed an order only to have 'em never receive it. Shipping is slow, even though they deliver the stuff personally from your local store.
www.atyouroffice.com - Absolutely top-notch office supply delivery. These folks could usually UPS stuff to me faster than Staples could send a truck to my house! Dunno who runs the place, but they've got my business.
www.jcpenney.com - Horrible. They've always got a deal going, but their selection is poor and I got more than my share of "sorry, we're out of that" emails. The only thing they've got going for 'em is that you can return stuff you bought online at the stores.
www.radioshack.com - Surprisingly good. Selection on their site is pretty good, and their products have always arrived before they promise they will.
www.buy.com - Good. Good feedback during order.
www.cdw.com - Very good. Also good feedback. They work exclusively through UPS, so it's easy to track your order.
www.mercata.com - Also a mixed bag. They've got some good prices, but we had some bad luck with a microwave they shipped us. Eventually we got our money refunded, but they should've known better than to ship a microwave in its original packaging via UPS.
www.amazon.com - The classic. They still do a good job, and they're the most responsive of the bunch, obsessively sending you emails telling you where your order is.
www.funagain.com - A great place to buy games online. It's basically a mom-n-pop shop, but they're very responsive, and they've got a good selection. Lots of stuff you can't find at your local Toys R Us.
www.pets.com - They've constantly got $10 off $10 coupons, so I can buy $10 worth of dog food for the $5 shipping cost. They're going through money like water, so I dunno how much longer they'll be around.
Favorite Coupon Sites
www.thedailydeals.com - Whenever one of those "too good to be true" deals pops up, they're the first to have it. I've got free subscriptions to Newsweek, Travel & Leisure, Wired, and Playboy just for filling out surveys, and I got a $95 DVD player with free Flooz.
www.amazing-bargains.com - These folks keep a database of the magic "coupon codes" to get discounts on stuff. Whenever I buy anything online, I check them first to see if I can get a discount, and I usually can.
www.bestbookbuys.com - Comparison prices of books. Always stop here before you buy a book, and you can save a couple of bucks.