For my first AG brew last weekend I used this little $0.99 app and was extremely happy with it. It calculates strike and sparge volumes and temps, IBU values, provides yeast strain data, and does brix/grav/ABV calculations.
There are a few other features, too, but IMO the ones I mentioned above are the brew day essentials. I tried messing around with the free trial of beer tools pro but I couldn't get past the confusing interface.
My question for you software vets: do your programs (promash, BTP, etc) offer more useful features for all that extra $$?