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One of the apps that I have on my AWESOME Verizon/Motorola Droid phone is the Aldiko ereader. It's fantastic! It has a lot of free books ready to download to my Android and read where ever I want. Plus, if I have a link to a downloadable epub file, Aldiko will get it for me!
[huge waves of warm, happy bookwormishness!]
My second shout-out has to go to Baen books and their webscription store. I've purchased several ebooks from them, and those books stay in my "purchased books" file online. I can go back to the store and re-download any book I've bought, and I can even download in a different format. So, all those John Ringo books I downloaded for the Sony eReader (which has now been stolen by the Munchkin) in the .lrf format? I can RE-download in the epub format with no problems, and Aldiko reads it beautifully!
Plus, Kindle is supposedly coming out with an app for Android phones soon, so then I'll be even happier!