FullPaint - to change fonts by using the keyboard instead of the mouse - holding down
Command-Shift-< (less than) will move you up your "list" of fonts. Command-Shift-> (greater than) will move you down your list of fonts in the font menu. You must have the font tool selected. To change the size of the font (again, first select the text tool), press Command-< to select the font in a smaller size and Command-> to select the font in a larger size.