Tweetcret.com

Tweetcret is an app that lets you anonymously post secrets to Twitter and follow the secrets posted by others. Provides more entertainment than therapeutic value. To follow other users secrets, follow Twitter user tweetcret.

Twitter Tees

Obsessed with Twitter? Share your love with the world by wearing a t-shirt from Eat.Sleep.Tweet. Slogans include "That’s what she twittered," "Veni, Vidi, Tweet," and "Eat.Sleep.Tweet." Shirts are only $14.99, but one is on special for $8.00.

CrowdStatus

The Twitter app Crowdstatus lets you create groups of people you want to follow on Twitter and then see them all on one page. For example, there is a CrowdStatus for the ReadWriteWeb crowd and another for the CNET crowd, but you can create your own groups, too. If you create an account on the CrowdStatus web site, you can also use the service to post updates to Twitter.

Twitta Rivva

Besides just being fun to say, Twitta Rivva is a meme tracker for the German twittersphere, providing info on popular posts, news, hashtags and more coming through Twitter.

YouTwit

The Twitter service YouTwit is another app that puts Twitter updates on a Google Map. To use the service, you enter in a Twitter ID and you’ll then see the location of those updates on the map. Locations appear to be determined by the place the person said when they registered instead of being real-time geo-positioned updates.

Feed Brightkite into Twitter

Mobile social network, Brightkite, lets you post location-aware updates to its services, which can then be integrated into Twitter. Brightkite users can also upload photos from their mobile phones using the service, which is also tweeted as well as posted on their Brightkite stream. In addition to Twitter, Fire Eagle is supported, too.

Twitter Quotient

The web site at Twitter Quotient will retrieve your Twitter stats - number of friends, number of updates - and then calculate your Twitter profile in three areas: a babble index (how must you post), a popularity index (how many people follow you/favorite you), and a Usefulness index (not sure where this comes from, but, for example, Scoble’s is "1 useful update for every 2,653.1 friends."

Twitter Portugal

The web site Twitter Portugal is a Twitter-related site for Portuguese Twitterers that makes use of the Twitter API to display a leaderboard of top Twitterers, most active Twitterers, the top sources from which the tweets arrive (e.g. the web, Twhirl, etc.), and more. The site recently began embedding the “Twitter Noise” ratio, Dave Winer’s “Spewage” ratio, mvalente’s influence scale, and Louis Gray’s noise ratio into their user profiles.

TwitterSnooze

Is a verbose Twitterer getting on your nerves? Or maybe everyone is tweeting about a conference you didn’t attend? Instead of un-following the users, you can just snooze them instead. With Twittersnooze, you simply enter in your Twitter credentials, the username of who you want to snooze, and the length of time for the snooze, which is in the range of one day to 30 days.

The Twitter Blacklist

The Twitter Blacklist is a site dedicated to identifying Twitter spammers, something they do based on a following to follower ratio. Think that new follower might be a spammer? You can check this site to be sure. Even better, a Greasemonkey script is available from Michael Klier which will put a banner at the top of a Twitter user profile if that username is identified as a spammer.

Update: This service is now closed.