Birdfeed, a challenger to the throne of iPhone Twitter clients currently held by Tweetie, might have the edge in some ways. It caches Tweets, so you can read your feeds even without wireless coverage, and looks super slick to boot.
The big draw is caching, but Birdfeed will also bookmark your place in a long feed so you can pop right back in later without having to scroll forever, as well as changing direct messages to a separate SMS-style section. We're sure some people will like and some people will dislike the latter feature, but we think it's a smart idea.
Birdfeed does cost more than Tweetie, at $US5 to Tweetie's $US3. It doesn't seem like much, but we imagine that could discourage a lot of potential buyers, since Tweetie is sort of the standard and of course works very well. Still, it's probably worth a look if you're a fanatic Twitterer. [Birdfeed, and download Birdfeed here (link opens iTunes)]