Apple sells refurbished Macs via their website at this link: http://store.apple.com/us/browse/home/specialdeals/mac. Everything on that site comes straight from Apple, with free shipping, and a 1-year warranty (same as new). If something goes wrong you bring it to the Apple Store or an Apple Authorized Service Center (also same as new). Typical savings: about 20%, though sometimes it’s a little more. I buy all of my Macs refurbished and pocket the savings. You should do it too.
Apple also sells refurbished iPads and iPods at a discount, as well as discontinued items from Apple and other manufacturers. See this link for that.