Credit:
With a database reaching back to December 2007, TweetScan allows you to download your Twitter archive at a page called TweetScan data. The benefits, according to TweetScan:
-Archive past exchanges
-Publish links and quotes
-Follow up on past projects
-Access offline
-View and reconnect with contacts
The only downside: like most Twitter apps, you need to enter your Twitter username and password to access the service. We consider TweetScan to be reputable, but there's growing doubt about whether this is really the best means of Twitter authentication.
More Twitter Resources From Mashable
-FOLLOW FAIL: The top 10 Reasons I Will Not Follow You in Return on Twitter