@Lindsey, I've only built Web apps for the iPhone so far. My son has built some simple apps, though. I'm working with him on some projects and have considered contracting or partnering with others to build apps. I understand and can do the programming but I tend to be better at coming up with ideas, designing the interface, and publicity. I always keep an idea list with me because I'm constantly thinking of them.
@crazy4boys, For planets and stars you might try SkyVoyager or SkyGazer.
There are a bunch of simple to do list applications in the app store that don't require setting a time. I wonder if one of those would be close to the way you like to work. My favorite is "Things" but it's kind of expensive.
We use Delicious Library for Mac to catalog our books. They put out an iPhone application that syncs with it but Amazon forced them to remove it. Amazon has some provision in their license about not doing mobile apps that connect with their service and Delicious Library depends on being able to do that @Gem suggested because you need Amazon to look up the details. I'm just glad I got my copy of Delicious Library for iPhone before they yanked it. :-)