3. Hercules
I think bringing Hercules in to the Marvel Cinematic Universe is a fantastic idea - as I've mentioned before - and prior to potentially joining the Avengers he could be introduced as a friendly rival of Thor's (a friendly rival whom gets in to fist fights with him a lot). Having delved in to Norse mythology with Thor, I see no reason why Marvel shouldn't want to introduce characters from Greek and Olympian mythology - a category that Hercules (who is Greek, not Roman, in the Marvel comics, as he is based on Heracles) falls in to. He is a real powerhouse who is a highly skilled hand-to-hand warrior and who possesses powers such as superhuman strength, speed, stamina, reflexes, endurance and durability, essentially immortality, a healing factor, an immunity to all Earthly diseases and a limited resistance to magic. As the son of another Skyfather (Zeus), but from a different pantheon, Hercules has been shown as a big rival of Thor - he defeated Thor when they first met, after Thor had been stripped of power, but Thor would then go on to save Hercules from Hades. The two brawled a lot, even after that, but Hercules has generally been shown to be an associate of the Thunder God and indeed other heroes as part of the Avengers (as well as numerous other heroic super-teams) and it would be great if he joined the MCU Avengers after initially fighting with Thor on the big screen.