I have several ideas:
Magmox - stone/magma race with ships that trail lava. When the lava cools, it provides an asteroid-equivalent barrier on the map.
Capacitor Aliens (no name yet) - Pure electricity. Grounded by different apparatus on their ship's bridge. Their ships store the first hit every x seconds as battery power, acting as both a shield, and a recharge.
Mining Aliens (Again, no name) - Mining vessel is ramshakle in appearance, but it's secondary ability is to capture asteroids nearby and then again to launch them at foes, or to use them like a fully powered Melnorme shot as a shield.
Magnetite Aliens (I'm terrible at names!) - Ship is a metallic cube, with smaller random cubes attached, just like naturally growing magnetite in nature. This ship tumbles seemingly at random on the combat map, which would look pretty cool in and of itself. When shot at, lost crew are actually fragmented off a magnetite chips that cling very close to the ship. If the chips are hit again by anything, they die a final death, but if the magnatite ship activates its secondary ability, if re-absorbs chips, regaining lost crew. Basically, dead crew form a temporary small field of interference, and can be reacquired at a substantial cost to battery.

Best look!!!

Simplest form of the idea...

Best combination of the two!
Ethereal Race (as in "insubstantial", not Ethereal as a proper noun.) - No ship idea, but their worlds on the Hyperspace map would be very hard to locate until you were right on top of them. Drop in-game hints to location, and then when you travel through such-and-such void in the map, BAM! Suddenly you're on top of 3-4 star systems that you didn't realize were there because the whole race is ethereal.
That's all for now. 
(Edit added pictures)