Our Best Buy closed down : (I got mine at Best BUy
It's really hard to find any site or store that undersells Apple. The prices on Apple products are usually within $25 to $50 of each other from store to store. You may find certain models that have been reduced in price from time to time.
Some available discounts that I know of:
1. Military exchanges (of course you must have an ID card to shop)
2. Student bookstores (academic discount)
3. Government employee and some other unions offer a small discount
And even better look at Apple Refurbished online. A new iMac can be purchased from $999 and comes with the latest operating system, a full twelve month warranty and Applecare's additional two year warranty is available on refurbished machines.
Refurbished Mac Computers - Refurbished Notebooks & Desktop Computers - Apple Store (U.S.)