You can obviously purchase your Mac and accessories from Apple Online or the Apple Store but Mac hardware is usually fixed in price, so it's worthwhile hunting around for retailers that give you a little extra with your Mac; especially a free two year extended warranty. This is a must; as more and more Macs are sold due to increased popularity, there's more chances of getting a lemon.
Here at MacDoc Ltd, one of our MacBook Pros had a faulty logic board after 18 months, the free two year warranty saved us a lot of money!
Costco: If you are a member, they are beginning to stock the latest 20" iMac and 13" MacBook Pro. They're being sold cheaper than the store that "never knowlingly undersold" and they come with a two year guarantee.
Below are recommended retailers that offer good value for money. Check out their offers and help support the MacDoc site.