FriendOrFollow.com
URL: friendorfollow.com
FriendOrFollow.com helps you manage your Twitter contacts. Find out who is not following you back, people you don’t follow you back, or see the list of people mutual follow.
TWITTER grader
URL: twitter.grader.com
Twitter Grader measures the power of your profile.
Find out the grade of your followers
http://www.twitter.grader.com/index.php?Action=TwitterFollowerList&UserName=psq
You can also get the list of the Twitter Elite.
SocialToo
URL: socialtoo.com
Get the ability to follow those that follow you automatically, unfollow those that unfollow you automatically, send messages automatically to those that follow you, and blacklist users to keep them from following you.
Also sends you a nightly e-mail giving you statistics of who followed you and unfollowed you during the day, and what your last Tweet was before that happened.
Also provides integration to identi.ca and Facebook.
Tweet Later
URL: www.tweetlater.com
Set tweets to be posted in the future. Send automated thank you notes to new followers, and automatically follow new followers. Get an email digest of the @replies you received.
You can also set up keyword alerts. They will email you a digest of the tweets that contain those keywords.
TweetBuddy
URL: www.tweetbuddy.com
TweetBuddy Prune is a simple, effective service for managing Twitter followers. It identifies those you are following who are not following you back, and allows you to quickly remove those who you don’t wish to follow any more.
tweeterfeed
URL: twitterfeed.com
Connect an RSS feed and automatically post new entries to Twitter.
twittercounter
URL: twittercounter.com
Provides a badge of your follower count on your site.
Also provides the top list of twitter user (by follower count).
twitthat
URL: twitthat.com
Bookmarklet (a button you can install in most browsers) to help you send a tweet with the link to the page you are on.
Twellow
URL: twellow.com
Provides a directory of twitter users, organized by category of interest based on the content of their tweets
Tools to shorten URLs
Twitter will automatically replace your URLs (using tinyurl.com) if they are longer than 30 characters long.
Other such tools (some with the ability to place ads, track clicks):
TweetGrid!
URL: tweetgrid.com
Create a bookmarkable page with a grid up to 3×3 that displays results from search.twitter.com
Twitter Search
URL: search.twitter.com
Twitter’s own search feature that displays all the matching results from the tweeter stream.
Twistory
URL: twistory.net
Add your Twitter backlog feed to your favorite calendar application and browse through your personal Twitter diary, making your Twitter history both fun and useful! Just start your tweets with either t or /t and Twistory will keep track of what you’re doing
Qwitter
URL: useqwitter.com
Qwitter e-mails you each time someone stops following you on Twitter
Big Tweet
URL: bigtweet.com
Post 280 characters long tweets (in 2 posts).
FlipMyText
URL: flipmytext.com
ʇxǝʇ ɹnoʎ sdıןɟ ʇı. Not sure that’s terribly useful, but sure is fun and will surprise people. And it is using real characters people can copy. Not restricted to use with Twitter, in fact.
tweetag
URL: tweetag.com
A different way to browse and search the tweet stream, using keywords.
beamagpie
URL: be-a-magpie.com
Make money by publishing some ads mixed in with your other tweets, or become an advertiser. It matches keywords chosen by advertisers and what you talk about. Costs are calculated based on # of followers and hotness of the topic, and they take a cut.
twitpic
URL: twitpic.com
You can post pictures to TwitPic from your phone, their API, or through the site itself
twictur.es
URL: twictur.es
Quickly upload pictures you can then post to twitter, or anything for that matter.