Twitter is my personal favorite social media tool. It works using text messages for direct messages, and there is an abundace of applications to use with it. All the resources are free to use (no paid apps).
You can upload an image, twileshare will then create a page with the download and tweet the link to your twitter account. Then people can make comments on the file.
Connect with people and create an inner circle. Great for keeping track of who you met and when you met them. Allows you to easily follow up with people as well. Mainly a salesperson's tool.
This is like a scheduler program, but instead of scheduling it decides when to launch your tweet. The intent is to not flood your followers, but I'm not sure why you wouldn't just schedule.
Basically housekeeping for your twitter account: Clean up and manage who you follow, find out who isn't following you, find out which inactive accounts you follow,
easily search inside your Twitter stream, Link Google+ to your Twitter account. However, you need a paid account for some features.
Get to know when your Twitter followers are online the most, so you can schedule your tweets for a good time.
The Archivist is a service that uses the Twitter Search API to find and archive tweets.
100MB Limit, ability to tweet your file, Or share by email, creates a short hash for your link.
Remi Sharp explains how to add a twitter feed to your blog using Javascript. The advantages of this method include avoid locking up your page or server and calls the twitter feed from the client not your server.
This is Identi.ca, a micro-blogging service based on the Free Software StatusNet tool. I like it because it's supported in ubuntu 10.10
TweetPsych lists creates a psychological profile of any public Twitter account and compares it to the thousands already in the database.
Allows you to create draft and scheduled messages. They charge you for more than 2 users.