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"
As long as you buy from an Authorized Apple reseller, you can get a perfectly good used computer or refurbished one for about half the price of a brand new one. And it will be fully tested and good as new. It might take some shopping around to find one, but it's a huge payoff when you do!
Sometimes you can even find an "open box" deal at your local retailer. That's when someone buys the computer, takes it home, and returns it within the store's return policy period. They can't resell it as "new", so they take a bit off the top. Could be anywhere from $50 to $150 depending on the time.
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.