Dell is well know for constant never ending (frequent expiration and then a new offer takes over) sales through affiliate site.
Stack coupons you buy on ebay or receive in email along with their special offers to save more.
Tons of "hot deal" sites like bensbargains, fatwallet, bargainshare, slickdeals, techbargains post all the hot dell deals all the time.
Keys to buying dell:
1) Watch for a few weeks dont just jump in. It may very well be cheaper in a day or two, or a week or two.
2) End of Dell quarters (April, July, October, January) produce the best deals typically, though end of months sometimes do too.
3) Dell home charges shipping but no tax to MOST states. Rare to get free shipping and is grossly (ebay gouging in fact) high like $100 a system that costs them $25 in actual costs. but you can have it shipped to your UPS or FedEx internet shipper account and pay less.
4) Dell business almost always has a free shipping offer, but charges tax to everyone.
5) Watch for stackable coupons
6) NEVER pay Dell to upgrade the ram or hard drive, and some other parts. They are MUCH cheaper to buy on the open market and upgrade later. (and sell (on ebay) the smaller parts that came with it to pay for a large percentage of the upgrade part!)
7) Watch for free/cheap monitor upgrades. Sell the monitor to pay for part of the system!

Don't transfer warranties on dell equipment you sell... you will eventually be branded a reseller and prevented from buying their hot deals in the future, at least through small business.
9) You don't have to be a business to buy through SB... Just enter you name as the company
10) You can get extra 3-4% back by using a click through company like fatcash or ebates or others in the form of a check about 4 months after you purchase through DELL HOME only.
It costs less to get a good dell then it takes to build one. Avoid the Celeron systems, the rest are all good performers.