Click below for pics of my models.  Accurail makes a great big ACF (American Car Foundry) type covered hopper.  Bowser makes an excellent small PS (Pullman Standard) type covered hopper.  Atlas makes a superb cylindrical hopper.

Accurail Covered Hoppers          (13 pictures)    HC-24, HC-38, HC-47
Athearn Covered Hoppers           (1 picture)      HC-27A
Athearn/Bev-Bel Covered Hoppers   (4 pictures)     HC-27, HC-38
Atlas Covered Hoppers             (5 pictures)     HC-7,  HC-13, HC-20
Bowser Covered Hoppers            (1 picture)      HC-35
Eastern Car Works Covered Hoppers (3 picture)      HC-3, HC-8, HC-37
Front Range Covered Hoppers       (10 pictures)    HC-41, HC-44
Intermountain Covered Hoppers     (2 pictures)     HC-43
Ramax Covered Hopper              (1 picture)      HC-44
Walthers Covered Hoppers          (2 pictures)     HC-16, HC-39