

Just discovered Twazzup this morning - the new real time search engine for Twitter. It's actually working and is nicely done showing your most popular Tweets and linking recent discussion to relevant tags.
Summize, launched last year, was already bought by Twitter last year and has already been incorporated into the Twitter Site two months ago. Nevertheless there are consistently new search engines appearing offering improved ways to better watch and structure your Twitter Tweets, Followers and Friends. Why??? ... is it only Twitter’s search advertising inventory? Obviously, these third party apps help Twitter itself to come up with new ideas which they can simply incorporate into their site.
Which Twitter Search Engines do you know of and which ones do you actually use?
On top of my head I can think of: