1) Tweetdeck
This tool is especially useful if you are new to Twitter and trying to figure out how it works and how to use it. Not only is Tweetdeck is an application that allows you to Tweet with individuals from your desktop, but with it you can also perform search queries and be notified when someone is searching for you. It's a great tool that runs on your desktop if you want it to. You can also use it to measure your Twitter buzz.
2) TwitterFeed
TwitterFeed is a free service that will automatically post your blog posts directly into your Twitter account so that your Titter followers can identify and read the blog posts that are of interest to them.
3) Uber Twitter
This mobile application is top notch when it comes to tweeting from your cell phone. Twitterberry, a common alternative for the Blackberry, seems to regularly freeze up according to users. UberTwitter, on the other hand, has a large following of users who love it. You can read tweets of those that you follow, reply to tweets and get direct messages all from your blackberry. It's a true timesaver for a business owner or marketing director that is on the go.
4) MrTweet
MrTweet takes care of you by giving you recommendations of who you should follow and also showing you those that are following you that you haven't followed in return. It provides awesome time saving tips that can get you following those that add value to your tweeting experience. A superb choice.
5) TweetLater
Automation for your twitter account will cost you a small fee, but it may be worth it. This little application gives you a lot of features, including scheduling your tweets, tracking keywords, sending welcome DMs to new followers, save and reuse drafts, and more. Just remember not to spam. It's not polite. And it's not acceptable!