At one time or another I had Dwarf Gourami's with Neon Tetras, Peppered Cory, Zebras, Glofish, and Guppies. I never noticed any aggression from the Gourami to the smaller fish. In a 20 gallon you still have plenty of space for more fish. In addition to the fish already mentioned, other good community fish for a 20 gallon are Rasboras, Glowlight Tetras, etc.
Is your tank fully cycled (mature filter)?