I just bought an iPad and so far the cooking apps don't impress me that much, though Bittman's "How to Cook Everything" is my favorite. For instance, you can navigate to butter sauces and get recipes for the usual suspects. I think this app is still in the iPhone format though, but it is compatible for iPad -- just smaller.
I'm not one for storing and rating recipes, so even though (Epi) Epicurious is slick and gets high marks, it isn't for me. With that said, the control panel searches on Epi work pretty well. Also Jamie Oliver has an app, but the recipes seem pretty limited. There is also All Recipes, which is growing fast that is probably worth a try. But the one app I am going to try is La Cucina Italiana. Again, it is only in iPhone format right now, and the iPad versions are only in Italian, but I think I would find their archive of Italian dishes useful to browse.
In the end, when I use a computer/iPad I usually just go to a search engine and perform my own search for recipe inspiration, adapt it, and then bookmark the recipe if it is worth it. I find Google/Bing searches to be more useful than most apps at this point.
k.