4. Bossk
Only glimpsed in one scene of the Original Series, where Darth Vader assembles a crack team of Bounty Hunters to track down the Millenium Falcon, Bossk could really make for an effective bad guy in the upcoming trilogy. In the expanded universe, Bossk is a legendary hunter of Wookies who often runs afoul of Han Solo and Chewbacca, resulting in a bitter rivalry between them. In addition, Bossk is also constantly competing with Boba Fett for bounties, almost always coming out the loser. While he shouldn't be the main villain, Bossk would be an interesting antagonist for the heroes in Star Wars 7-9. Physically imposing, crafty, and vicious, Bossk could be a sidekick to the main villain or could be operating alone, but either way it would be nice to see him featured more prominently in the upcoming films.