Tweetreach will search for current tweets you sent by hashtag, link, keyword or other search operator and see how far out it spun. It only goes back 50, due to some cost that twitter charges to see the full report. You can apparently buy this report form them.
Searches did take a minute or so to compile and I did not get results from a tag I know I used in April. So I chose one I used today to see the results. If you combined the reach of Corvida and myself from the right side listing of people that carried that term, we hit over 5000. not bad at all.
They give a nice graph showing tweets, retweets and replies to give you an idea on how the trend is spreading. Then another wheel graph of total exposure.
It is also a good way to see who is using your content as their own feed on Twitter. I certainly found some 🙂