Here are the ones I know of off the top of my head:
BrewPal - full featured app for developing recipes and taking you through the brewing process. There are some timers and whatnot in there to help you time mashes and hops additions, as well as fermentation stuff, but I have trouble using them personally. BeerXML import/export supposedly coming in next point release.
BeerAlchemy Touch - Mobile version of BeerAlchemy for mac. Syncs with the desktop version. I haven't used Beer Alchemy so I cannot really tell you much about how it compares.
BrewMath - Made by the same guy who does Beer Alchemy. This has been on the app store for a long time now. It is a collection of calculators for common brewing stuff, like mash volumes, strike water temperatures, IBU calculations, etc.
Brewing Alarm - This is a free app for managing all the time-related tasks in your brewing process. It has the ability to import a BeerXML file and automatically set all the related alarms for mashing, sparging, hops additions, etc. Of course the very first recipe I tried loading into it had First Wort Hops, which it doesn't appear to handle, so those additions were missing. But apart from that it works very well and is dead simple to use.
There is also an app that integrates with BCS control systems so that you can control it remotely over your phone. I don't remember the name off-hand, but I remember it being very expensive for something you can easily do in safari.
