Part of the beauty of Twitter is the whole universe that has emerged around the API. While the simplicity of the service itself makes it a joy to use Twitter really comes in to its wn once you start using the applications that have sprung up around it.
So, down to business. I've written about most of these before and it's interesting to note that my preferences haven't changed - perhaps it's a case of sticking to what you know.
Quotably allows you to track conversation threads relating to a Twitter username you specify, it shows both conversations started by that user (with related replies) and those threads the user has contributed to. This is especially useful in tracking any answers to a question you may have asked and getting a screen dump of them all in context.
Twitter has a habit of not referencing the correct tweets in a thread so Quotably let's you re-organise them so that they appear in the correct order.
Quotably has also recently introduced a new feature which tracks the most popular things happening on Twitter in real time.
TwitThis is an easy way to post a link to any page to your Twitter feed and can be used via a browser bookmarklet, a button on your page or even a WordPress plugin. TwitThis gives you a number of options to choose from for telling the world what you are doing such as: Reading, Looking at, Responding to in order to give a bit of variation with your Tweets. An example looks like this:
There are a number of Twitter search tools out there but Intwition is different in that it is designed to search for URLs. Bloggers can perform ego searches to see who's been discussing their blog. A good twist on this is the "reach" stats - not only can you see who has been posting links but also the total number of Twitter users potentially exposed to that link. You can even subscribe to your query as an RSS feed.
Another great way to track tweets about specific topics is to use hashtags: simply a word proceeded by a hash character, e.g. #hashtags. Tweets that include these tags can then be collated in order to get an overall picture of conversation about a particular subject. There are a couple of sites you can use to track them but hashtags.org gives by far the best information.
There's my favourites so it's my turn to keep the ball rolling and tag someone else. If we're playing by the same rules that Julian set then whomever I choose should not duplicate any of the tools already mentioned here or in the other posts in the series - this could start getting tricky.
I'll tag Mark Dykeman of the Broadcasting Brain, over to you Mark.