(Tweetie 2 has been bought by Twitter and renamed Twitter for iPhone 
X )
Tweetie was rewritten from the ground up with a fast and powerful new core and now offers the most polished mobile Twitter experience around.
Seamlessly handle multiple Twitter accounts
Explore all of Twitter, from your own timeline and mentions, to the favorite tweets of your followers and friends
Full persistence: more than just caching tweets, Tweetie 2 restores your entire UI if you quit or get a phone call
Fantastic new offline mode. Read, tweet, favorite, follow, save to Instapaper and more even when you don't have a connection. Your actions will be synced as soon as you go back online
Full landscape support (configurable of course)
Live-filter your tweet stream
Post photos and videos, even configure your own custom image host
Vastly improved compose screen with recent hashtags, @people picker, URL shortening and more
Compose screen multiple-attachments manager
Drafts manager ensures you never lose a tweet (and you can even send drafts to Birdhouse)
Link Twitter contacts to Address Book contacts
Follow, unfollow, block and unblock from multiple accounts simultaneously
Saved searches sync with Twitter.com and the upcoming Tweetie 2 for Mac
Autocomplete recent searches and Go-to-user
Threaded Direct Messages and improved conversation navigation
TextExpander integration
Rich integration with Follow Cost, Tweet Blocker, Favstar.fm and more
Edit your own Twitter profile
Specify custom API roots on a per-account basis
Nearby map view
Translate tweets
Preview short URLs
Safari bookmarklet support for easily sharing links
In-app rich text email composition
Tons of little things, including improved avatar caching, auto-refresh, refresh-all, seamless Twitlonger support, hashtag definitions.
United States
Comments and Reviews
A really nice Twitter client for the iPhone. I used Tweetie before and this new version is just so much better. Love the "pull down and release to refresh" function.