What is currently listed at your Twitter Connections setting? (It is located at Profile > Connections). Are those application used often by you or you simply allows all application to access your twitter account?
I have just clean up some application that I did not even know I have allow it. Currently, I have some new Twitter applications which I am still trying out their service and some old trusty twitter applications which I used them from time to time.
Here are some of my old applications:-

SocialOomph – Here you can schedule you post, this is one of the most important feature you could use if you would like to be appearing on twitter update all the time but do not have the time to tweet every 30 mins. Not only that there is option to vet users, direct message user when someone adds you. It also shorten your URL.

TweetMeme - Of course I have this, it is the quickest method whereby you can RT someone blog post. This is a great way of sharing and this is what Twitter is all about.
Twitterfeed - This is a must have Twitter application for all bloggers. As the name implies, you will import your feed to your twitter account. Many bloggers does get tones of traffic via Social Network.
Twitpic - Although I do not use this often, but people who like to share picture should always have this and tones of phone apps are compatible with this twitter apps.
ManageFlitters - You need a way to mass manage users, and this is what I find to be one of the easiest and have best available functions so that you don’t simple unfollow some important friends.
Bit.ly – Simply one of the best url shortener, you can even tweet directly from their site. Best thing is that their url shorterner is just automatic and you get stats out of all the URL that you have shortened with them.
Twibbon - Yup, I have created a Twibbon, I believe 2 years ago to show our love to Malaysia.
New Twitter Application

Twtamigo - This is something new whereby you have credits for following new people and you can choose to offer from 1-10 credits for each people who follows you. Although it is a little buggy at times.
urli.st – A way of sharing links with a group, it is not quite a twitter application but you can login with your twitter account.