He's easily the strongest Avenger of all time. Granted immortality by the Apples of Iddun, Thor can summon thunder and his hammer Mjolnir is one of the most powerful items in the Marvel universe.
Hulk
Bruce Banner's alter ego resulting from gamma radiation exposure, is the benchmark of strength in the Marvel Universe. He is one of Avenger's strongest members just in sheer physical strength.
Blue Marvel
Blue Marvel/Adam Brashear is one of the strongest Marvel heroes. The only reason he is somewhat unknown is that his character disappeared from comics for a long time, due to racial issues.
Scarlet Witch
The daughter of Magneto can create and alter universes at her whims. Once she destroyed 99% of all mutant powers with a mere whisper, which makes her one of the strongest beings.
Doctor Strange
Strange, as the Sorcerer Supreme (in comics), is a master of the mystic arts. Assisted by the Book of Vishanti, his spells can alter the fabric of reality.