Amazon.com plans to unveil a new, improved version of its Kindle reader tonight amid growing competition from Apple's iPad and others seeking a piece of the hot electronic book market.

The next-generation Kindle is smaller and lighter than the previous version, with faster page turns, longer battery life, built-in Wi-Fi, and other upgrades. It's the same price as before, $189, and for the first time Amazon is introducing a Wi-Fi only version, for $139.

That kind of price point could make Kindle attractive to the mass market consumer. But anyone hoping for a color display or touch screen will have to wait. Amazon said those features — which are central to the popular iPad — aren't part of the new Kindle.

"Most books are black and white," said Amazon vice president for Kindle Ian Freed, in an interview at Amazon's new headquarters in Seattle's South Lake Union. "What we're focused on is making the reading experience better."

Read on for more details and a photo gallery.

Here are some of the key specs on the new Kindle, which starts shipping Aug. 27:

—21% smaller body with same 6-inch diagonal display.

—15% lighter, now 8.7 ounces. (The Wi-Fi version is 8.5 oz.)

—Still 1/3 inch thin.

—20% faster page turns.

—50% better contrast with the E-Ink display.

—Longer battery life. Up to a month with wireless turned off (compared with 2 weeks on the old version), and up to 10 days with wireless on (compared with a week on the old version).

—Double the storage. Can hold 3,500 books, compared with up to 1,500 previously.

—Built-in Wi-Fi.

—Available in graphite or white.

—Browser upgrade. The "experimental" web browser is now faster and easier to navigate, according to Amazon.

—Voice guide. Kindle's "text-to-speech" feature now allows for voice navigation of the menu options.

Freed said Amazon has been thinking about adding Wi-Fi to Kindle "for a long time," and said the Wi-Fi feature gives Kindle users more flexibility.

"If I move out of 3G coverage into Wi-Fi coverage, the Kindle just figures it out," Freed said. He added: "If you use it at home and work, the Wi-Fi (only) version works just fine."

The $139 Wi-Fi Kindle is another sign of the e-reader price war going on right now. Amazon just last month slashed the price of its standard Kindle to $189. Barnes & Noble cut the price on its Nook reader to $199 and has a Wi-Fi only version for $149. Sony recently lowered prices on its lineup of e-readers, which now sell for $299, $169 and $149. Kobo has a reader for $149.

The frenzy of price cutting among the single-purpose e-readers followed the introduction of Apple's iPad, a multi-function tablet computer that has its own electronic reader application and associated bookstore. (Wi-Fi only iPads start at $499, and Wi-Fi + 3G iPads start at $629 with data plan sold separately).

Despite the success of the iPad, Amazon has consistently stuck to its electronic-ink technology, saying it's better for reading than the LCD screens in the iPad and other devices. But there's been intense interest in whether Kindle will ever add color or touchscreen.

Asked about the potential for color displays for Kindle, Freed said: "We haven't found a way to add color in a way that improves the reading experience," adding, "A lot of technology is still in the labs, but we'd certainly look at that."

Freed said Amazon could have added touchscreen to the new Kindle, but said it would have required adding another layer of glass in front of the screen, which would have distorted the display. He gave no indication of whether Kindles would include touchscreen in the future. (Amazon reportedly acquired a New York touchscreen technology startup called Touchco earlier this year, but the company has never confirmed it.)

Amazon also emphasized it will continue to push for e-books priced at $9.99 or less, despite pushback from some of the major publishers on that. Amazon said 510,000 of the 630,000 e-books in the Kindle store are $9.99 or less, including 80 New York Times bestsellers.

Oh, and there's a new leather case for Kindle with a built-in, retractable reading light that recharges on the Kindle's battery ($59.99 for the case, $34.99 without the light).

Update: Here's the official Amazon press release.

Amazon CEO Jeff Bezos tells USA Today that Kindle books, which according to Amazon have already surpassed hardback books in sales, could soon overtake paperback as well.

I predict we will surpass paperback sales sometime in the next nine to 12 months. Sometime after that, we'll surpass the combination of paperback and hardcover. It stuns me. People forget that Kindle is only 33 months old.

Images:

Follow my updates on Twitter.