If you want to save some money on your next Mac, consider a certified refurbished unit from Apple. Discounts are typically around 15% but can be over 30% on some items. There is a selection of iMacs, MacBooks, iPods, iPads, Apple TVs, nearly every product that Apple makes except the iPhone, and most are the current model or the one immediately preceding it. These are units that have been returned under warranty and refurbished, both electronically and cosmetically. They are thoroughly tested, and in the case of battery-powered devices, they have a new battery installed. They come with the same one-year warranty as a new product, have the same eligibility for the AppleCare extended warranty and are shipped free. I’ve purchased two refurbished Macs and have been very pleased with them. I don’t think the odds of getting a “lemon” are worse with an Apple refurbished product than with a new one. After all, they go through a lot more testing after they are repaired than one fresh off the assembly line.
I think the key here is “Apple Certified Refurbished”. There are also 3rd party retailers that offer “refurbished” Macs, but I’d be much more cautious about buying one of these.
The selection of refurbished products at Apple seems to turn over pretty fast. Check the listings frequently for what you want and be prepared to act quickly when you find it.