I recently found, through a knowledgeable source, a link to a list of companies that use Twitter: Twibs. Since I'm still deciding whether this is a personal blog or one focused on business, this is exactly what I have been hunting for.
From the New York Times Bits blog, here is a brief look at applications aiming to "organize and filter the hundreds of conversations, from impromptu snowball fights to political scandals, under way at any given moment."
Listed are brief descriptions of TweetDeck, StockTwits, and TweetBeep.