Twitter Mashups are arriving at the plenty. With some you struggle to see their worth, but recently I have discovered some that I can immediately see some clear uses for:
Twitter Grader may at first just seem to be satisfying the ego of Twitterers, however with no stats available within Twitter it could help measure the impact of a campaign that incorporates Twitter, as could Tweetburner which enables you to measure the number of clicks on a URL you post within a tweet.
Other of my favourite Twideas:
TwitterFeed automatically posts a Twitter when you add a post to your blog or other RSS feed.
Twellow a directory of Twitters by subject.
Twitt Earth shows Tweets as and where they are coming from, not really useful but one of my favourites and makes a great screensaver.
On my iPhone I use Twinkle which lets you filter twitters from 1 to 252,000 miles from you.
This post is clearly not an extensive list of Twitter apps, there are plenty of sites that do that. I wanted to share my favourites and my excitement over the amazing Twideas that Twitter inspires and will continue to as the microblogging phenonemum continues to grow.