I'm a big fan of the Honor Harrington series, but there's ton's of others. Vorkosigan saga is pretty awesome, and not at all your typical space opera. They have a lot of older works too, from people like Andre Norton or Larry Niven. Basically, it's a huge publishing house that focuses on the fun parts of the genre, and offers it's works directly for very reasonable ebook prices. Most books are five or six dollars...they also allow readers to buy advance copies of works for $15 months before they're released to the general public.