I suppose this is a kind of obvious choice, but aside from Darth Maul, most people don't know what you're talking about when you say Zabrak. Of course, who wouldn't love running around as a dude with horns and spikes jutting out every which way from their head? Plus, apparently if you're a good Zabrak your tattoo-like skin turns blue, or red if you're evil. Then again, both of those concept are subjective when you start getting into shades of gray.
What I really love about this race, however, is that they can fit well into just about any role on either faction. In fact, I'd feel safe in assuming they would fit into even the unannounced classes, too. As far as voice work goes Zabrak's don't sound any different from most of the other races. So their variant voice work probably wouldn't be required, which is always a bonus.
Lizard people! Well, okay it'd probably be more accurate to call Trandoshans reptile people, but I couldn't resist. Variety is an important factor in my picks, as is choosing races that aren't too obscure.
Something I've considered as a possibility is that Wookiees may be exclusive to the Republic, which would make Trandoshans an Empire exclusive race on the opposite end. The primary reason being that neither of the species have ever gotten along too well. Actually, many Trandoshans have been known to enslave Wookiees. There's also a lore precedent of the Trandoshans siding with the Empire in the original trilogy era of stories.
Some cool facts: Trandoshans possess infrared vision, similar physical strength to the Wookiees and can slowly regenerate lost limbs. Both of these traits make for very obvious racial features. And I personally think playing as a Trandoshan Bounty Hunter would be an absolute blast.
Okay, I've been here before, but I just really cannot let go of the Droids. BioWare was able to make a fan favorite out of HK-47, and the concept of playing a cocky evil (or good, even) robot is just far too appealing not to include on my list.
Smugglers, Bounty Hunters and some kind of spy or assassin are the obvious class applications for a Droid. The problem becomes classes beyond those, because giving a battle Droid too much sentience runs the risk of all-out rebellion. Then again, the Empire has far less living people to recruit into some kind of standing army. The traditional stupid combat droids aren't very effective in battle because, well, they're dumb.
The concept I've been rolling around in my brain has been that of a Droid steeped in personal story. What would make a much more interesting story? To me, it would be a lowly combat (or some other variant) Droid slowly yet assuredly gaining sentience somehow. Maybe through a freak accident, or by some outside force intervening upon your character. My point is that, whatever the current reasons are for Droids being hard to make happen, it can always be written around in some way or another.
I could honestly go on and on about potential races, and the Star Wars universe has plenty to offer. However, I'm sure you've all got your own picks and thoughts on the subject, and I can't wait to see them.