You can use Mozzarella cheese on toast as Mozzarella cheese does melt pretty good on toast and tastes really great on toast as well.
Even Cheddar cheese sis another great cheese to melt on your toast which also gives the toast a good flavor as well.
Other good cheeses to melt on your toast are Fontina cheese, Havarti cheese, Gruyere cheese and Monterey Jack cheese.
If you want a milder tasting cheese that also melts great you can use American cheese or even young Gouda cheese.
If you want a more bolder and more complex flavor of cheese on your toast along with a great melt, then using a combination of sharp cheddar cheese as well as a nutty and savory Alpine cheese like Comte cheese or Gruyere cheese are great choices of cheese to melt on toast.
Medium sharp cheddar cheese is also great and brings a richer flavor for melting on toast.
Young soft or semi soft cheeses like Swiss cheese, Havarti cheese or Gruyere cheese are great for melting on toast and have a high moisture content that means they are especially adept at turning molten.
Even Pepper Jack cheese is great for melting on toast and gives the toast a spicier twist.