We had success with zinc supplements. We have male and female factor infertility, so DH had lots of sperm tests over the course of our TTC. His initial count was <1million sperm ('normal' is approx 20million, I think it's per ml). After taking zinc, his next count was 4 million, and the count after that (about 6 months later) was 11 million (and the cycle we conceived our beautiful son on).
DH is taking zinc again, and we're TTC #2 and he and I are convinced that it had a very beneficial effect last time.