Amazon today responded to Barnes & Noble’s price reduction of the Nook by reducing the Kindle to $189, from $259. The move was presumably in response to Barnes & Noble’s introduction of a $149 Wi-Fi version of that company’s eReader, the Nook.

Barnes & Noble also reduced its 3G version of the Nook to $199. The 3G versions of both the Kindle and the Nook get their wireless connections from AT&T.

The Kindle’s new price falls squarely between the two Barnes & Noble devices and seems to signal the beginning of a price war in the eReader space. It remains to be seen if Sony will join the race to lower prices. Sony makes a pair of eReaders that sell for $199 and $169, but both need to be connected to a computer via a USB cable. Sony’s only other eReader is 3G capable but costs $349.

The next front in the eBooks market will perhaps be waged on the content side, with Apple in the space via its iPad tablet and accompanying iBooks application and service.