You'll likely get a host of different suggestions/remedies from posters. My baby had a AWFUL diaper rash for the first 8 months of his life, probably from the Pampers diapers we were using. We tried everything under the sun, both prescription and over the counter. They first thought it was a yeast infection, but it was not.
The only thing that took it away for us. We switched to Seventh Generation diapers, rinsed out the wipes with warm water, dried the area with a wash cloth, and applied this brand of zinc oxide:
http://www.allegromedical.com/skin-care-c535/zinc-oxide-ointment-1-oz-tube-p192199.html
It finally cleared up within a week. We continue to use only that zinc, 7th Gen diapers, and rinse out the wipes to this day and my baby is now 8 months old.