Where are some good places to train in fire red to beef up my team for the Elite 4 rematch?

Question

please note, i've covered the 7 islands top to bottom already....

Answer 1

At the Indigo Plateu itself; Repeated battles against the E4.

Repeat run-throughs of battling the E4 with no HP/PP Restoring items, no Legendary Pokemon (unless they are apart of the team) or Over Leveled Pokemon, such as a Lvl. 80 Starter that guarantees success. Train the weaker once in order to have an evenly solid team.