Hydra Miniatures offers a good selection of retro-bots as part of it's Retro Raygun line.
(Size comparison w/figure from Rattrap)
Wargames Supply Dump has a couple of robots as part of their Dick Garrison line.
Pulp Figs also has some robot that come straight from a mad scientist's lab.
Killer B Games include a hovering 'bot in their G.A.F.D.O.Z. line.
('Bot comparison: Left, Rattrap's Robot Type II; Center, Killer B's GAFDOZ4; Right, Hydra's Robot Legionnaire)
And Rattrap have a robot in their .45 Adventure line of pulp models.
(unpainted Robot Type II)