Flat bench bicep curl.. I have never done these and not been tremendously sore the following day. Yet I never see anyone doing them, and they are never promoted. Heck, I hardly ever do them myself. They are not an ego lift, 20lbs is more then enough weight.

I'm not saying soreness is a gauge for a good workout but it's obviously a sign of trauma to muscle fibers. I do them after my heavier barbell or dumbbell curls sometimes. I really should do them more often so I'm not always crippled the following day.

Here is a image i found from google image search

http://www.building-muscle101.com/flat-bench-lying-dumbbell-curl.html