Amazon.com announced today a price drop on its flagship Kindle 3G + Wi-Fi e-book reader, providing you're prepared to receive ads and "special offers" on the device. The Kindle 3G with Special Offers, available to order today at $164, is now the lowest-priced 3G e-book reader, says the company. The original Kindle 3G is still available at $189.

Five weeks ago Amazon unveiled the first ad-supported e-reader, the Wi-Fi-Only Kindle with Special Offers at a price of $114. In his hands-on review of that device, CR's Paul Reynolds noted that the ads were not terribly obtrusive:

The Kindle with Special Offers, the new low-priced version of Amazon’s e-book reader, keeps its advertising and deals from interfering with the reading experience, as Amazon CEO Jeff Bezos asserted in an interview yesterday. And in over a week of using the device, I’ve found the offers to be generally welcome--or at least inoffensive, since they’ve been discounts from Amazon on items I’d consider buying.

Today's announcement follows on the heels of Barnes & Noble's unveiling of a new Nook e-reader, the Simple Touch Reader, at an event yesterday. A Wi-Fi-only device, the new Nook is priced at $139. B&N also dropped the price of the previous-generation Nook 3G to $169.

It may be no coincidence, of course, that a day after B&N's announcements, Amazon has dropped the minimum price of its key competitor to the Nook 3G to $5 less than the older B&N device--which remains the only Nook (other than the Nook Color) that you buy get until June 10, when the Simple Touch Reader ships.