An absolutely epic Traveller campaign that lets your players be what they've always wanted to be deep down : SPACE PIRATES!
It's a great framework where the players are given Letters of Marque in order to support the ambitions of the most recent king of a shattered empire. You can play it as the being the plucky underdogs helping the little guy stuck between two empires or say, screw this, thanks for the ship and take off to do your own thing. Or any combination thereof! Start with the war crimes! See what happens!
Three books plus a companion and a host of supplementary material will have your players YARRRRing for months or years if you so choose.