What are the most essential Twitter apps ever created?

OneForty looks like the best site yet to provide a categorized list of Twitter Apps.

While OneForty requires an invitation to join and so is not available to everyone yet, I wanted to provide what I think is one of it's most valuable features to the general user: a "best of" list of apps organized by category they call "essentials."

What do you think? Are these the  most essential Twitter apps out there? Here's their list as of late September, 2009:

Desktop

• TweetDeck

• Tweetie for Mac

• Twitterrific

• Seesmic Desktop

• DestroyTwitter

• Twhirl

Mobile

• Tweetie

• SimplyTweet

• twidroid

• UberTwitter

• TwitterFon

• Gravity

Business

• CoTweet

• HootSuite

• TweetLater

• PeopleBrowsr

• Twitter

• EasyTweets

Networking

• Mr. Tweet

• WeFollow

• Who

• Friend

• Twitter

• UnTweeps

Entertainment

• Overheard.it

• Twittervision

• Twistori

• Twitter

• CelebritiesThatTwitter

• Post Like A Pirate

Monitoring

• Objective

• TweetBeep

• PeopleBrowsr

• OneRiot

• Collecta

• Radian6

Media Sharing

• TwitPic

• Qik

• Blip.fm

• twt.fm

• Screenr

• yfrog

Link Tools

• Bit.ly

• Tweetmeme

• Eventbox

• twitterfeed

• Backtweets

• TwitThis

Analytics

• TweetStats

• Twitter

• Twitalyzer

• TweetVolume

• Tweetrush

• Follow Cost

Random

• Peekr

• Post Like A Pirate

• Flip

• Portwiture

• pici.me

• Oh My Science