actually sand benders are real, they were shown in the desert where the library was found in book two, although it is unclear whether sand bending is a form of air or earth bending
Gooosh, guys, the sand benders are earth benders that have just specialized in bending sand. Remember, Toph could also bend sand, but she just had trouble "seeing" because the sand created a "fuzzy" mental picture for her.
She was probably the greatest bender, besides the avatars, because she was an extraordinary at earth bending, but she even invented metal bending and could sand bend. Also she did this all blind.
*a billion white girls post pictures doing the same thing on tumblr*