Price is one area where the Kindle shows some vulnerability. Amazon’s two electronic readers on the market now have relatively high price points, with Kindle 2 at $299 and Kindle DX at $489. Sony’s new lineup of readers includes a $199 device.

And Asus, a Taiwanese maker of cheap netbook laptops, has floated the idea of an e-reader in the $160 range.

Amazon CEO Jeff Bezos has defended Kindle’s pricing in the past, saying it incorporates the cost of the technology that goes into the devices, including the specialized E-Ink display.

But it seems clear that the Kindle will face continued price pressure.

“The cost of the display component is high and sales volumes are still modest, yet consumers demand and expect ever-lower prices,” wrote Forrester Research analyst Sarah Rotman Epps in a recent report.

Epps found that many consumers are holding out for electronic readers costing $98 or less.

Some Kindle competitors, Sony among them, have embraced an open e-book format called ePub, which allows digital books to be read on a variety of devices.

In doing so, they’ve set themselves apart from Amazon, which restricts digital books to its Kindle readers and associated iPhone application.

Meanwhile, Google, which is engaged in a massive project to scan millions of library books and make them available online, has been steadily forming partnerships with the likes of Sony, Barnes & Noble, and others to distribute its digital titles.

Many of these scanned Google books are free, public-domain books, so they don’t generate revenue, but they have given Kindle competitors a way to boost their e-book selections. Amazon emphasizes new-release books and bestsellers for Kindle. (Amazon opposes Google’s proposed class-action settlement with book author and publisher groups, which provides the framework for the search giant’s book-scanning project.)

Looming over this young e-book market is Apple, which is rumored to be developing a tablet-like computer with electronic-book-reading features. Apple’s entry into the market—given the company’s success with the iPhone and other consumer electronics—could shake things up for Kindle and other players.