For iOS I like BrewPal. Easy for recipe formulation, you can export to BeerXML, and decent enough customization. There is also a brew timer that works well. I also like BeerSmith on my laptop and then sharing the recipes to my iPad which runs BeerSmith app on it.
BrewPal is much cheaper if you are looking for something to get you started without much out of pocket and then later you can buy BeerSmith and import all of your recipes if you want more tools (ie water adjustment calculator, inventory management of ingredients, multiple equipment profiles, etc.)
BrewPal is great to get you up and running building recipes and getting you through the brew day. It also has a great BJCP guide built into it that is a quick and thorough reference.