Winged Mercury dime, but the image would have to be changed enough so that it would easily, without looking at coin composition or year on it, be seen as not the same. I love the ones minted but think a slightly different on would be goodl
Eagles. Double, half, full, anything with a non-trivial face value. Heck, bring back half and full unions.
The Trade Dollar If I remember correctly, the Trade Dollar still stands as the only American coin that was de-monetized.
Anything gold. And the Standing Liberty Type 1 quarter. Because, I missed the controversy the first time.
None...why bring back what has already had its day in the sun? This is why I so hate the re-releases of classic series as commemoratives. Instead, hire someone who can create a new classic design. If, OTOH, you are asking what obsolete denomination I would like to bring back, then, bring back the three cent piece and get rid of the cent.
Lincoln wheat cent, duh. And im not talking the soft struck, weak detailed, crap that are the zincolns. Im talking about full blown copper planchets struck from dies made from the 1915 master hubs. I want to see the mint actually engrave Lincoln's fully detailed hair and beard again!