The quickest and most accessible in my area is CA baby diaper cream at Target.
You can also use olive oil, coconut oil (a natural anti-septic), and several diaper brands make their own diaper cream. People also love CJs BUTTer, but I have no experience with that.
We use Homestead Baby Balm. It usually takes away diaper rash by the next diaper change.
We also have some CJ's Butter and California Baby rash cream. I would rank Homestead Baby first and CJ's Butter last. I do like CJ's as a hand cream, though.