Based upon several discussions over the last few days, it's become clear that the formats supported by the iPhone were unknown by many. I've started a table over on the iPhone page of the wiki.

I've put in the formats which I know of and care about to some extent. If you all can add any you know about or care about, we'll have a fairly clear reference to anyone who wants to know about the format capabilities of the iPhone.

I'm guessing the iPad's table would be very similar, but until we can confirm whether each app is supported, I won't make any adjustments to the iPad page.

Edit away!
I've updated the wiki entries for iPad and iPhone to show the most recently available applications for differing formats on those platforms:

iPad

iPhone
Thank you, nikkie.
Good day,

non-DRM ePubs can be imported to iPad through iTunes too.
I've updated both of these to reflect new development from B&N, Kobo, and txtr.