Here are a few (along with their relationship to "Team Arrow" and other fun facts) and why each of these comic book heroes would work well on the CW's Starling City!
The Answer Is...
The Question had also worked quite a bit with the next candidate....
A Gem Hidden In Plan Sight
Ted assumed the mantle of the Blue Beetle, but had been unable to get the mystic scarab that powered the original, so, instead used technology (including his BB-gun and flying ship, the Bug) since Captain Atom #83 (November, 1963, by Steve Ditko).
The Arrow series has even mentioned Ted Kord himself, as well as his company, Kord Industries, so why not have the man swing into action himself?
Flowers Are Pretty
Cowboys and Indians
DC even had established the Vigilante as a separate hero, who teamed up with the JLA.