SF e-book site by Random House; they're giving away the first books of some series as *free* PDFs, to get people hooked.
The first five include Kim Stanley Robinson's "Red Mars", which is probably the best hard-SF book I've ever read -- a very realistic epic of colonizing Mars, which also has well-drawn characters and interesting political and ecological ideas.
There's also Naomi Novik's "His Majesty's Dragon", which my wife says is a kick-ass combination of Patrick O'Brien style 19th-century seafaring plus dragons.
