The rest of the article is merely for historical purposes as Amazon seems to have re-implemented this wonderful policy, woot!BEGIN OLD INFO, MAY NO LONGER BE VALID AS OF April 16th 2013:
Well, this is a sad day. Amazon will no longer refund the price difference if they lower an items price after you purchase it.
Their nice original policy:
Post-Order Price Guarantee [original policy]
Amazon.com’s prices for released items will change from time to time based on a variety of factors. If Amazon.com’s price for an already-released item decreases within 30 days after we ship the item to you, we’ll be glad to refund the difference in price if you contact us within that 30-day period. Please click the Contact Us button on the right side of this page, and be sure to have your order number handy so we can assist you.
This was a very nice policy as sometimes you might order an item from Amazon and the next day it would be drastically cheaper, meaning you overpaid. Sometimes the price difference could be hundreds of dollars if for example it was a laptop, DSLR, or high-end computer parts (SSD drives, video cards, etc.)
Their new policy eliminates price protection for customers:
Post-Order Price Match Policy [new policy]
With the exception of TVs, we do not offer post-order price matching when an item’s price drops after you buy it. Our prices regularly change, and the price you paid when your order shipped was the lowest price we were able to offer at the time. We consistently offer competitive prices on everything we carry because we know low prices are very important to our customers.
This is a real bummer as the Post-Order Price Guarantee was one of the ways that Amazon really stood out above the crowd (NewEgg, TigerDirect, Wal-Mart, etc.)
I contacted Amazon to see when this new policy went into effect, but the customer service representative would not say. 
END OLD INFO, MAY NO LONGER BE VALID AS OF April 16th 2013.
Amazon 30-day Post-Order Price Guarantee 2013,
Strange… As of today, 04/16/2013 they still do the 30 day price guarantee. I know because i just did one. Something I bought a couple of weeks ago dropped in price and I sent Amazon customer service a note about it, quoting item, order number and price change amount. The refunded the difference within a couple of hours. NOTE: for this to work you must have bought the item directly from Amazon and the price drop must be on the exact same item and be done by Amazon. So noticing a better price by a 3rd party seller or having bought from a 3rd party seller then noticing a lower price offered by Amazon if you buy from them is not going to do you any good. If you buy directly from Amazon and then Amazon drops the price on the item within 30 days, you’re in luck!
Hi Aruba, that is great news!
That is certainly how it used to work so I am glad to hear that they have re-instated their 30-day price guarantee and I will verify this the next time I have a qualifying order.
Best regards,
-JD