The current storybundle includes a few complete trilogies, rather than the usual book 1 (and then you're on your own getting the rest), as long as you pay at least the bonus level, and I'd strongly recommend Machineries of Empires to anybody who loves space opera and/or excellent worldbuilding.

storybundle.com/trilogies

(I'm not involved in any of this, I've just loved reading it)