I use OdoBan on mine. I put a cup of it in the washing machine when I load my clothes in. It seems to help. For nasty odors, I'll pretreat with it.
I've also had some luck with Cupridyne (which is marked up and sold here as Pooph!, if any of you have seen the infomercials). It's great at getting rid of intractable odors, but it seems to take a LOT to make a noticeable difference.