For large battles I really like Warrior Heroes by Two Hour Wargames. That, or Battlelore/Command & Colours.
For Skirmish games we use Rattrap's pulp system, using the Fantastic Worlds supplement as starting point. In addition to our existing Retro-Sci/fi campaign we are just starting a D&D style campaign set in the Wilderlands of High Fantasy.
I've converted D&D's classes to FW archetypes and am impatiently waiting on BA to see its Archetypes. In my conversion, Rank 1 = level 1, Rank 2 = level 5 and Rank 3 = level 10. I envision Rank 4 = level 15 and Rank 5 = level 20 but am interested to see how Richard is handling above rank 3.
Magic will be D&D magic, modified to fit.