first off, sorry if I'm doing a thread that's been repeated before, but I wanted to put my thoughts into this one.
current pirate ships: pillager, rogue, cutthroat, reaper, corsair.
Basically, come up with ships that fill missing roles (like cruisers and what not).
I'll start: Pirate Brute. Brute is a nasty ship that is only encountered on larger scale pirate attacks. Brute is a rather unique ship because it's the pirate capital. In my mind, the brute would be a combat/fleet support ship that is a nightmare to any planet it attacks. I think it would start around level 3 and move up from there.
Pirate Ravager: not many ideas to this one yet, I think it would be a assault cruiser or carrier, but I'm not sure