You should probably check out the modding compendium: https://docs.google.com/document/d/1lVP ... Q6pH8/edit
That saying I'd recommend Overhauls like: Arsenal+ and Multiverse. You can find them in the modding compendium
if you just want some Graphical Improvements then: Better Planets and Backgrounds, Crew Graphics Compilation and Pretty Shields.
if you want to try things like new Ships and stuff its pretty much based on what you think looks pretty, so just click around and look at the ships and decide which one you like the most.