There are a multitude of websites that have recommendations for various educational iPad apps. There are very few that are consistently solid. Richard Byrne's iPad Apps for School is generally a great resource and he posts several worthwhile apps each week. He also has a companion site Android 4 Schools which I'm sure we'll need to use in the future as more and more Android devices come into our classes.
Today, MindShift, a blog that I usually follow for it's engaging and challenging thinking on education, posted 5 Great Math Apps for Grade School Kids. As I read the descriptions, I found myself agreeing with them. Three of the five apps are paid ($2 - $4), but if they perform as described, would seem to be the kind of apps that help build math fluency in a manner that goes beyond a digital flash card.
I further realized that MindShift has a page for educational apps, and the nice thing about it, is that they don't post a lot. A few ideas every few months - kind of like us.