The big automotive/trailer reflectors work well like the one found here:
http://surplustrailerparts.com/image...460R_large.png

The little dinky reflectors supplied with bicycles are mostly just to comply with CPSC rules and are not very effective in my opinion. Yes, they work, but not great, but better than nothing.

The reflectors on pedals do work well at times, as do the side facing reflectors on spokes that most of us remove from our bikes.

But, yeah, use both passive and active lighting and reflectors.