Announced April 14, 2010, the Library of Congress will digitally archive every tweet from Twitter since March 2006.
Next, Google will offer a searchable timeline of Twitter tweets. The service will be called Google Replay. I’ll try to include more when available but until then, you can see tweets on a search by selecting the + Show Options, then select Updates from the list of options. Of course, you have to search a subject first. Have fun!