The odor neutralizers that have proven most effective for me are (1) 20 Mule Team Borax added to the wash, or (2) this cat litter additive:
http://www.amazon.com/gp/product/B000TSO20W/ . For a small load, I use about a level Tablespoon of the cat litter additive; it's quite amazing. I'd try borax first, though, as it's less expensive.