I actually thought that Thane Ector had a lot of potential (and his story did have a nice set-up, I just think it was kind of condensed to fit the sumer six-issue double publishing schedule, and it kind of suffered for that). Think about it. They were not simply sentient bacteria, They were a race of powerful eternals (the most perfect creation of the Celestial Gods) evolved from the worst there is in nature. I think a lot could be done with that.
I've endlessly defended that the Gatherers (from the same period as Thane Ector), in the hands of the right writer, could end up being some of the Avengers most interesting adversaries, but there are plenty of other foes that never amounted to much that I could see rising in status if given a chance. I've already mentioned Graviton and the Zodiac Cartel, but there are others.
- Alkhema - Due to the spy background of her human template, an even more ruthless and unpredictable Ultron, and the living proof that the female is the deadliest of the spieces.
- Lord Templar and Pagan - I never liked much the triune understanding nor Mr Tremont, the third part of this equation, but I always thought that this dichotomy of order and caos personified had potential to cause big trouble for the Avengers. Plus, they were both powerful as hell, which is always a bonus.
- The Thunder Guard - An alternate reality Nazi Avengers from the pages of A-Next. Always wanted to see them face the present day team.
- Count Abyss - This one never faced the Avengers. He was a one-time villain in the pages of the Infinity Watch, but I really liked his name and looks, and the fact that he was more of a cosmic scheemer and manipulator rather than a conqueror, but he still seemed to be pretty powerful.
Peace