EmailTwitter - With this service, you can send tweets to Twitter from your cellphone without incurring SMS charges.

GroupTweet - Allows you to post private message to a group of Twitter friends.

Hashtags - You can add tags to your Twitter posts with this service.

HelloTxt - This service enables you to update Twitter, a host of other micro blogging sites, and social networking sites Most-Networked-Executives with one click.

LiveTwitting - Helps you cover a conference live on Twitter. Similar to liveblogging, only cooler.

SecretTweet - Post to Twitter anonymously. If you really need to.

TweetCube - This service allows you to post files on Twitter. Files that can be shared include .zip, .rar, .pdf, .jpg, .png, .gif, .mp3 and .txt.

Twitxr - Another neat way to post a picture on Twitter, Facebook, or Picassa.

Twitter Feed - This tool allows you to send your blog atom or RSS feed to Twitter.

TwitterGram - Post an mp3 on Twitter using this service.