As most Twitter users know, it is extremely important to shorten a URL if you are going to post a link. There are a variety of URL shortening services available, but one of my personal favorites is bit.ly.The site not only allows you to shorten a URL, but also tracks the number of clicks, tweets, and social network mentions a link receives. And, best of all it is free.
Twitalyzer is also good. It provides a wealth of measurements for reach and engagement, and even provides tips on how to improve your Twitter reach and performance. If you would like to know the hot topic of the moment on Twitter, check out Twitscoop. Twitscoop allows you to view a cloud of trending topics, instead of the ten you usually see on Twitter.
Twubs is a useful application that allows you to register a hashtag and create a social group around the topic. This helps minimize the likelihood the hashtag is in use by someone else, and creates a place for discussion.
If you want to see how all of this works, follow Knotice on Twitter!