Wondering what e-reader to buy for a holiday gift? Certainly the Kindle, now available for just $139 for the standard model with a 6-inch display, is likely to top many lists, given the price, the Wi-Fi connectivity, and the backing of the world’s largest bookseller, Amazon. A version with 3G costs $189, while the Kindle DX, with its larger screen, costs $379. But the Kindle is far from alone among e-readers, and the website eBookNewser has a guide to 15 e-book readers. These include the Samsung Galaxy Tab, Apple’s iPad, and a variety of other contenders.