I'm old school,so i'll throw some dark horse teams in here....
The Defenders:They once fought The Avengers to a standstill...
The Justice Society:They had a member who could defeat just about ANY of these teams by himself(The Spectre).
"The Spectre has also played a pivotal role in the Crisis on Infinite Earths and Zero Hour storylines. In both cases, in the final struggle against the main villain (the Anti-Monitor and Parallax, respectively) the Spectre was the only hero capable of standing against the villains directly, allowing the other heroes time to put a plan into action that would destroy the villains once and for all."
"The Spectre is the most powerful known being in the universe and is capable of virtually any feat. His powers have vastly increased over the years. At times the Spectre utilized the mystic Ring of Life to perform feats beyond his powers."
http://en.wikipedia.org/wiki/Spectre_(comics)
The Defenders:They once fought The Avengers to a standstill...

The Justice Society:They had a member who could defeat just about ANY of these teams by himself(The Spectre).


"The Spectre has also played a pivotal role in the Crisis on Infinite Earths and Zero Hour storylines. In both cases, in the final struggle against the main villain (the Anti-Monitor and Parallax, respectively) the Spectre was the only hero capable of standing against the villains directly, allowing the other heroes time to put a plan into action that would destroy the villains once and for all."
"The Spectre is the most powerful known being in the universe and is capable of virtually any feat. His powers have vastly increased over the years. At times the Spectre utilized the mystic Ring of Life to perform feats beyond his powers."
http://en.wikipedia.org/wiki/Spectre_(comics)