Some unofficial concept art has purportedly revealed the team line-ups for Captain America: Civil War. Why even bother prefacing it with Captain America anymore? It's Civil War, drop the Captain America. While I'd say take this with a grain of salt, Marvel has habitually leaked concept art before ie The Winter Soldier and Age of Ultron that were spot on, so these line-ups may not be too far from the truth. It's still just speculation though.
Captain America and Iron Man will be leading their respective teams, obviously, they're the leaders.
On Iron Man's side, who I imagine would be on the pro-registration, or pro-government side, we have, War Machine, Black Widow, Iron Man, Black Panther, who will be making his first appearance in Civil War and Vision.
However on Captain America's side, who I imagine would be on the anti-registration side, we have, Hawkeye, Ant Man, Sharon Carter, Captain America, the Falcon and what appears to be some sort of drone-like variation of his pet bird, Redwing and the Winter Soldier.
Missing from the team line-ups are Scarlet Witch and Spider Man, I'd guess that Scarlet Witch would be on Captain America's side, while Spider Man would be on Iron Man's side. No word on the big green guy, but I wouldn't be surprised if they use him in lieu of Goliath.