you cannot curve a single polygon.
to make a curve you would need atleast two, but thats not really a curve. try 10 or more polygons to see things smooth out. But yeah you can use deformers, the non-linear curve works, or even a lattice deformer. but there is always the standard old modeling by moving verts.

If all else fails you can extrude an edge along a curve and that would give you a curved result.