1. Buy Online — but NOT from Apple
Apple has an online store, but there are a number of discount stores that specialize in Apple, and they are often about $100 cheaper. Apple ships their new computers directly to these stores for sale, so the product is exactly the same.
(I guess Apple wants to maintain a reputation with their prices? I don't know.)
Buy from a discount Apple store like MacMall.com, and use the money you save on some cool software, or a backup drive or something.
2. Buy an Older Model
Once Apple starts selling a new model/version of the MacBook or iMac, last year's model drops significantly in price. And it's only a year "old", so you won't be missing out on too many features. After all, just the day before it was the latest and greatest!
I recently found this search on Amazon.com
3. Buy "Pre-Owned" or "Refurbished"
Finding a Mac computers sale just takes a little time researching online. But if you take the time, you might find the best buy on Apple computers.