Although both of my children are out of diapers, I highly recommend Triple Paste for diaper rash to anyone who asks. 

When my son was 1-2 years old, he was really prone to ear infections, and one year they gave him an antibiotic that gave him the most horrible acidic diarrea ever.  I mean, this kids butt was raw.  Triple paste healed it up in less than 24 hours.  Works on the toughest diaper rash - and it really soothes.

Most drugstores carry it - it comes in a white box/tube with royal blue lettering.  If you've got a friend with a child battling diaper rash - be a hero, and tell them about Triple Paste.  They will certainly thank you for it.  :)