German WWII half tracks are good. Or some of the early open topped Assault guns (Stug I, Marder etc).
Also Soviet BMP's, if you can find them in 1/35, with the tops removed look kinda orky. Russian stuff has that bulky, solid, but will get the job done look, rather than NATO kit with looks too good.
Also British WWI tanks have a very 40K look to them, I've always thought of trying to convert one as a Battlewagon.