I just re-read "Underworld," and had enjoyed it so much in the past, that I'd made plans to display a scene from this series:
and I think to add the most prominently missing characters you could take your pick from:
Bria Tharen (Rebel Agent also key in the Han Solo Trilogy, Han's ex-girlfriend)
Sardu (bounty hunter with the Jawa commandos)
Jozzel Moffet (chick that was majordomo to one of the other Hutts)
This was a seriously fun comic! Sure there are a lot of them with potential, but Underworld rocks. They could always make Han and Boba Fett, cartoony-style like the art in the books, but I'm not really interested in more versions of these guys again.