Tweet Library is an excellent app by Riverfold Software which allows you to "curate tweets". You can create collection of tweets and publish them online, keep an offline cache of your tweets and favorites, filter your timeline and sort tweets by date. It's a great companion to your default Twitter client. From my review:
Tweet Library is an app meant for letting you archive, collect and filter tweets. It’s great for conference tweeting, it’s a good tool for blogger when a new iOS beta comes out and they need to group tweets about new features, it’s a great app for users wondering “what happened to that tweet?”. Tweet Library is a searchable local archive of your Twitter activity.
The new 1.1 update brings full support for iOS 4.2, meaning multitasking and persistent state. It works perfectly. The app now also contains a bunch of additional filters for pictures shared on flic.kr, instagr.am, and plixi.com. The developer also introduced lots of performance improvements and fixes.
Tweet Library is available at $9.99. If you use Twitter on a daily basis and you care about keeping a personal record of your tweets, it's well worth it. Check out the full changelog below.
* Added your own Twitter lists in addition to lists you follow.
* Added flic.kr, instagr.am, and plixi.com to pictures filter and inline thumbnails.
* Added multitasking support for iOS 4.2.
* Added shorten links command when composing a tweet.
* Added colored badge in corner of tweet for favorites and retweets.
* Improved retweet confirmation alert to include username.
* Improved tweet text display and line wrapping.
* Fixed initial download sometimes stopping short of 3200.
* Fixed bug refreshing timeline that caused some new tweets not to appear at the top.
* Fixed bug cleaning up older tweets from the timeline (keeps recent 5000 now, 1000 for search, and everything you posted or collected).
* Fixed difficulty tapping in filter to edit query text.
* Fixed web links being difficult to tap.
* Fixed not being able to follow a conversation from a Twitter search result.
* Fixed collections not highlighting right away when you tap them.
* Fixed duplicate saved search when updating the query text.
* Fixed copy short URL button after a publish sometimes copying the full URL.
* Fixed duplicate and unnecessary errors when loading the embedded web browser.
* Changed menu on messages to just show DM or public reply commands.
* Changed direct message posting header to "DM:" instead of "To:".
* Other minor bug fixes and improvements.