1. Bufferapp – When you are browsing the web and come across interesting content you may not want to share it all at once. So what you do is click the buffer button and buffer will create tweets based on the article and schedule them at appropriate times for delivery. A really handy tool.
2. SocialBro – A very useful twitter analytics tool. Filter by number of followers, find the people that are not tweeting, filter by language, find out who you are following that are not following you back, send a tweet automatically to new followers etc.
3. Vizify – Find out your top followers, how often your tweets were retweeted, geographic impact and much more.
4. Hootsuite - I’m sure you’re using this already but just in case you’re not! It’s a very comprehensive tool and more features are added all the time.
Any other good ones to add?