Reader Andrew Berrigan left a very informative comment on another post, and I wanted to be sure you were aware of it.
In his comment, Andrew mentions Alfons Schmid’s Notebooks app for the iPhone and iPod Touch. He gives a great summary of its features, and it was enough to convince me to purchase the app. I look forward to putting it to use. Note that it is not only useful, it is also budget-friendly: when I downloaded it, it was only $3.99.