Plugins that I installed specifically for Movable Type 6, and plugins provided with Movable Type 6 that I disabled by removing them from the /plugins directory.
New plugins installed for Movable Type 6
Asset Handler v1.0
To import the numerous image files and plain downloadable files as assets into Movable Type, because assets did not exist in Movable Type 3.33.
I had to perform a few minor tweaks to this plugin to get it to work in Movable Type 6. I found out later that Jay Allen has a v2.0 fork of the plugin. I should try it out and see if it works in Movable Type 6 without modification.
Hot Date v2.1.1
Replaces the functionality provided by the old UpdateAuthoredOn plugin.
More Listing Framework Columns v1.0.10
This plugin adds more columns to Movable Type admin pages which make use of Movable Type's Listing Framework.
To replace functionality provided by the older EntryList v1.0 plugin.
Publish Queue Manager v1.3.6
This plugin provides a simple user interface in the Movable Type administrative system to view, change priority, and delete publishing jobs from the built-in 'Publish Queue' system.
This plugin has one notable flaw: If the PQ Manager plugin is installed in a brand new Movable Type 6 installation that has never published a job to the Movable Type publish queue or run the tools/run-periodic-tasks script, it completely breaks the Movable Type installation.
Once a file has been published to the publish queue or the run-periodic-tasks script has been, this plugin is an essential tool for monitoring the jobs currently in the Movable Type publish queue.
Replacement for the older SQL v1.52 plugin.
Website & Blog Organizer v1.0.1
This plugin makes it easy to reorganize the website and blog hierarchy, particularly if you do not like the website/blog hierarchy created by Movable Type 6 during an upgrade from a Movable Type version that did not have websites (any version of Movable Type older than Movable Type 5).
Default Movable Type 6 plugins removed to disable them permanently
The following plugins were moved from the /plugins subdirectory to a /plugins-disabled directory I created specifically to hold these plugins. In case I ever decide I want to reinstall one of these plugins, all I need to do is move the plugin files back to the /plugins subdirectory.
Feeds.App Lite v1.22
No desire to ever republish feeds on my blogs.
Never heard of mixi (a form of OpenID?) authentication for commenter sign-ins.
Never used Textile 2 for text formatting when writing entries and doubt that I ever will.
Widget Manager Upgrade Assistant v1.1
From the plugin description: "This version of the plugin is to upgrade data from older version of Widget Manager that has been shipped with Movable Type to the Movable Type core schema. No other features are included. You can safely remove this plugin after installing/upgrading Movable Type."
No need for a Wordpress importer now or ever.