CrowdBooster
CrowdBooster is a great tool for analyzing your tweets for the week or the month and looking at them graphically, seeing how many times different tweet were retweeted, and what kind of impressions you had the potential of making. (Note: I say potential, because it does not mean that many people saw the tweet. Just because I have over 4,000 followers, does not mean they see everything I tweet. However this does give you a general idea of which tweets you put out that score better with your followers.)
The horizontal shows how many times a tweet was retweeted, and the vertical shows the number of impressions. (this is just a total of the followers of everyone involved in retweeting the message. If you have one person with 20,000 followers retweet you, that will add 20,000 to this number) By hovering over the dots, you can see which tweet the dot is referring to. You can also choose to look at the data in a table format.
Crowdbooster has some other benefits worth exploring, like top retweeters and recommendations on the best times to tweet to name a few. Best of all this is free to play with and explore at the basic one account level.
Social Mention
Social Mention is a great social search engine that will help you find where people are talking about you or your brand, after all it is only by knowing where your audience is speaking about you, are you able to engage them. Like google alerts you can set up an alert to let you know when people are talking about you.
