Twitter List Directory

With the ever broadening social media landscape, here is a Twitter Directory by Topical Index Heading @ http://mashable.com/twitterlists

Here are some others social media lists or directories which you might be interested in as well:

Federal gov agency blogs http://www.usa.gov/Topics/Reference_Shelf/News/blog.shtml

Link of Gov agencies on Twitter: https://alicemfisher.wordpress.com/2010/08/08/government-agencies-gov-persons-on-twitter/

Find State & Local Governments on the Web here: http://www.statelocalgov.net/index.cfm