Now that the iPad has been released, there are three kinds of apps in the App Store: apps made specifically for the iPhone (and iPod touch), apps made specifically for the iPad, and hybrid apps that include both iPhone- and iPad-optimised interfaces in a single download.
The problem is that, while the iTunes Store provides a convenient button for browsing either iPhone-only apps or iPad-only apps, the iTunes application makes it much harder to tell the difference between the two types. If you select Apps in the iTunes sidebar, you’ll see a list of all downloaded apps. But by default iTunes doesn’t differentiate them, and when your iPad is connected, the Apps tab for your iPad provides no way to view just the iPad-specific apps.
However, there are a couple of ways to distinguish your iPad and hybrid apps: click on the Apps item in the iTunes sidebar (your iPad doesn’t need to be connected) to view all downloaded apps. Choose View > As List. Then select View > View Options and check the box next to Kind (or Control-click any column header in the Apps view and choose Kind); this action adds the Kind column to the list (see ‘What kind of app is that?’).
Click on the header of this Kind column, and your apps will be sorted by app type: iPad app, iPhone/iPod touch app, or iPhone/iPod touch/iPad app (click again to invert the sort order). Unfortunately, iPhone/iPod touch apps end up between the two types of iPad-optimised apps, so it’s a bit of a hassle to view all apps with an iPad interface. But it’s better than nothing.
The other way to view apps in such groups is to choose View > As Grid and then choose View > Grid View > Applications. This shows you a graphical view of all your downloaded apps, grouped by app type.