Robert Kroese’s Dream of the Iron Dragon [Amazon link] is free through the end of today on Amazon. This is a great series, and getting a taste for free is a good way to see if is something you might like. There are five books in the series, so it will keep you busy for a while. Check out my review, and go grab your free copy today!
If this is the kind of thing you are into, Rob has an asteroid strike trilogy in the works too.