TweetBeep
Awesome tools that notifies you every time your name, brand or any keyword you choose is mentioned on Twitter.
FriendOrFollow
Find out A) who’s following you that you’re not following back and B) who you’re following that isn’t following you back.
Twitter Tools
WordPress plugin that allows you to pull your tweets to your blog. It can also update your Twitter status every time you post.
Ping.fm
The easiest and fastest way to update your status on Twitter, LinkedIn, Facebook and over 40 social media sites.
Qwitter
Are you losing a lot of followers? This fantastic tool can help you understand why.
Twitter Grader
Do you want to find out how good is your reach and influence in the Twitter community? This tools can help you.
TweetDeck
An amazing Twitter client that allows you to sort your tweets into
replies, topics, groups, keywords, etc. You can even filter the results.
HootSuite
In my opinion, the coolest and most powerful suite of Twitter tools out there. Track your stats, manage multiple Twitter accounts, monitor your brand, schedule tweets, update all your social networks and much more.
TwitPic
Cool Twitter app that allows you to send photos on Twitter.
TweetStats
A great tool that gives you a very valuable insight on your Twitter marketing campaigns.