Ideas suggested thus far:
Sell clothing
Grow medical Marijuana
Sell basements
Sell FAR stuff
Rent it out
Sell miles
Nightclub
Open a Religion Shoppe
Sell Vanilla Reloads
Sell suits
Open a filtered Internet bar
Sell alcohol
Offer job counseling
Sell jewelry
Sell silver
Tutor people in the art of churning
Open a brewery
Bingo
Geirus factory
Baked goods
Small gift shop
Candy shop
Gown "Gemach"
Consulting service for other basement entrepreneurs.