Kool-Stop Salmon Continental. I wouldn't use anything else on steel rims.
http://www.sheldonbrown.com/harris/b...ml#continental

(Though you may be able to find them cheaper elsewhere.)

Seriously, they work better than anything else, particularly in cold weather -- though they still won't make a steel-rimmed 3-speed stop fast in the rain. They're a little bit softer than ordinary pads, which means that rusty/pitted rims will chew them up faster. But they're worth it.

If you object to the all-over-orange color, you might try prying the old rubber out of the metal holders you've currently got and replacing it with one of the Kool-Stop inserts -- but it's probably not worth the effort.