I've used this brand's anti-mildew paint with outrageous success in
poorly ventilated baths with teen-age girls taking "showers for hours"

They have a fairly comprehensive DIY page that helps you figure out
what you need, also.

And, as someone else mentioned, hit up a real paint store. Quality is
a step above and worth the extra price. And, amazingly, the people
behind the counter usually REALLY are in the know.

http://www.zinsser.com/Products.asp