I got an iphone recently and predictably I've been very interested in acquiring all sorts of applications. Here's my (ranked) list at the moment:
Google, Mobile Fotos, Night Stand, Yummy, FullScreen
Google Earth, RK Free, NYTimes, Skype, Zillow
Not that Useful
RedDelicious, Trulia, iNapkin, RedLaser
(Suggestions to add to this list would be welcome.)
The above list was current as of the time of this post.
My continuously updated list is here.