*** See #315100: Allow to add JS/CSS libraries (sets of files, settings, and dependent libraries) for the patch to put jQ in core! ***
The jQ module allows other modules to register jQuery plugins in a central repository, and allows administrators of a site to enable or disable specific plugins globally.
The concept behind this module is to create a basic hook structure for jQuery wrapper modules, allowing other modules using these plugins to invoke them in a consistent fashion.
(Drupal 6 version only): You can also simply add new jQuery plugin files in your /plugins or /sites/example.com/plugins directory, and they'll be added to the registry. Then, for example, if you upload jquery.example.js, you could just jq_add('jquery.example'); and you're off. Additionally, if you have a .js and .css file with the same base name there, they'll both be added with the same call. Caveat: if you have two plugins with the same base name, there are no guarantees which will be added to the registry. Better off defining a hook_jq function in that case (see below for information on that).
Kudos to jjeff for his work on the jQuery Plugin Handler (JQP) module that inspired this latest functionality.