The best book I have ever read (and continue to re-read) on writing is "On Writing Well" by William K. Zinsser. Mostly the first half of the book - it's incredibly valuable.
It's also available in paperback (for $10!). If you're serious about learning to write well, it's well worth putting down the Kindle and going "old school" on this one.
Yeah, I'm just not from the US so I don't like to wait for the package to arrive, pay extra for the shipping, then have it clear customs, etc. Kindle provides instant gratification and all that :-)
I'm not in the US either, but patience is a virtue, and good things come to those who wait. The Kindle is great, but don't let it form the limit of your world.
http://www.theamericanscholar.org/writing-english-as-a-secon...