Brewzor is excellent, but it's much more useful if you're an AG brewer. When I was doing extract it wasn't as useful since I didn't use most of the calculators. Since I moved to AG it's an invaluable tool for me, and something I have on my belt where I don't have to run to my computer for Beersmith. It's free currently as well since it's in Beta, but the developer announced on his site that he is indeed working toward full-on Brewzor 2, but it may be a while before it comes out.
I have an old iPhone 3G that I often use simply as a timer on brew day since I don't have any care if it were to get wet and I'd thought about buying BrewPal since it looks quite nice and is only 99 cents, but the reviews were tanking it - waaay too many complaints of crashing and wiping out the entire recipe database so I passed. But, it doesn't matter cause I've been very happy with Brewzor and wind up just using my Droid 2 for the timer now.