Tweetizen is a tool in beta that provides groupings around topics, or lets you create your own. From their own site:
Use Tweetizen to create twitter groups, and you’ll be able to stay on top what is happening in all your areas of interest. Imagine having instant access to breaking news and the latest tweets on news, politics, technology, gossip, fashion etc. all in one place, rather than having to create multiple twitter accounts just to be able to find what you want.
You log in with your existing Twitter account and start creating groups based on keywords (tags) or user ids of other Twitter users. I clicked into some of them and they have a good set of starter lists made. Such items as SEO, Technology and sports statd out right away as a great stream of information. It was such a simple process to do and you find yourself making a bunch of groups right away.
Reading on it seems they have some new capabilities coming down the line also:
We have some big plans for Tweetizen. Our future releases will include the ability to:
* Create groups with family and friends
* Share your groups with others
* Ability to re-tweet and directly contact other tweetizens
* Embed your groups on other websites
* Search for other groups