The big mailorder outfits like MacConnection and MacZone do offer some great deals, but I'd avoid MacMall (have for a decade in fact); read this forum. P.S.: ClubMac and OnSale are divisions of Mac Mall.
Check MacPrices for the latest prices from all the major vendors, including Apple.
As for AppleCare, considerable savings can be found via PriceGrabber; just make sure you order the package well before the end of your initial one-year warranty, as the AppleCare documentation has to be mailed in when purchased from third party vendors.
5 Tips For Getting The Best Deal on Apple Purchases