unfortunately it has to be the supermarket at Globus, I say unfortunately cause it's the most expensive ever but the cheeses and the Charcuteries are killers...
Boucherie du Molard for top quality meat.
Brauniman at Crouge is a good meat joint too.
Get to Ferney Voltaire (just across the French border) for the Saturday morning market.
And Plainpalais for a good flea market with extras (on Wednesday and Saturday)
La Halle de Rive is small and friendly. It's a little cheaper than Globus but still eye-wateringly expensive.