Looking for recipe formulation, IBU/SG calculations, brewing timers, inventory control, etc.
A bonus if the app renders my iPhone waterproof(wortproof).
Brew Pal is an excellent program for storing recipes and doing some calculations for things like IBU and gravity, which is what I use it for. I purchased it the day after I bought my iPod, just because I wanted to support homebrew apps, turns out I love it and use it on every brew day.
It allows easy email export of BeerXML, which makes storing recipes off the iPod easy.
It's also $0.99, which is not a good reflection of its value, I'd pay $4.99.
Kent Place Software produces some useful brewing apps for iPhone and Mac. They also have an iPad version in the works. I've used their Beer Alchemy Mac software for awhile.
BeerAlchemy Touch is their iPhone version. It's a bit pricey at $14.99, but provides wireless syncing between the mac version and the iPhone version, which is really handy.
Brew Math is also handy, and only $2.99. Not as fully featured as BeerAlchemy, but is described as a "powerful brewing calculator in your pocket."
Hope that helps!
My Brew works great. It let's you track your brews, calculates abw/abv/calories, provides overall brew stats, brew timers, etc. iTunes Link
I'm a little late to the party, but the best one I've used is iBrewMaster. It's currently available for $7.99 for the iPod/iPhone edition and $10.99 for the iPad edition. Rather than regurgitate all the features, take a look in the iTunes store here and here for more details. Overall, it has worked the best for me in managing the process from start to finish. I especially like the alerts functionality when I have multiple batches going at once.