Well, you'll be spoilt for choice. I know many Genevans may not agree, but "Les Armures" goes down very well with visitors. It serves typical Swiss food (notably fondues), as well as an international menu. It's in the old town, and fairly picturesque.
Others you might think about "Palais de Justice", "Chez Papon" (not that Swiss, but good), "La Mère Royaume".
If you're an American not familiar with Europe, remember that the menu prices are net prices, including tax and service. You don't have to leave anything more than what's on your check, though it's usual to give a few francs or Euros, if you're satisfied (but nowhere near 18%).