Marco Arment’s Instapaper application is, according to Arment, expected to be available on or very near the release date for the iPad.
Of note in Arment’s blog post is how difficult it is to develop and release an application (wait, are they apps or applications on the iPad?) without having an actual iPad to test with. Arment uses a slick little cardboard-based template in tandem with the emulator that ships with the development kit to get a feel for how it might be to use Instapaper on the iPad, but, obviously, that’s not the same as working with a legit iPad.