The first book I read on my Sony Reader was "On Basilisk Station" by David Weber. There were two main reasons for this. 1. I had read it before and liked it and I wanted to be sure that my first book read as an ebook was one I liked. 2. It is available as a free ebook at Baen Books.
David Weber is accounted a master of military science fiction and I would have to concur with that assessment. This is the first book in the Honor Harrington series that now numbers well over a dozen. They are loosely based on the Horatio Hornblower books and there are many parallels beyond the shared initials.
If you like sci-fi books with a hard-assed space captain, then this is a book you will enjoy. If you like plenty of action... ditto. After having read all the books in the series, I will say that they follow the same formula. There is a slow build-up until all hell breaks loose at the end, and you get to find out which of the characters you have come to like gets killed. Still, they are great stories. The writing is crisp. The universe is interesting.
I would have to recommend Honor Harrington to any fans of space science fiction, and this is one of the better books in the series.