This deal at Adorama is live again: they are discounting the Vivitar 58mm Three-Piece Solid Neutral Density Filter Kit to $4.99 (regularly $13). It comes with an ND2, ND4, and ND8 filter.
Many entry-level Canon lenses take 58mm filters (including the EF 50mm f/1.4, 85mm f/1.8, or EF-S 18-55mm, 55-250mm).