Here are the classes I have so far for a B/X Sword & Sorcery game:
Fighter - as B/X
Thief - as B/X
And three more I am currently considering:
Mystic - spellcasters from the eastern kingdoms which have strong traditions in mind-affecting sorceries. An illusionist with a coat of paint.
Borderer - a variation of a Ranger. There would be some overlap with some of the other classes though so I am still thinking about this one.
Shaman - spirit totems, etc. This one would be largely taken from one of the BECMI gazetteers with some OD&D Druid thrown in.