I have a jQuery Plugin that I use myself which modifies the selected value of select items on a page. In my own code the plugin automatically executes as soon as it is included in the page this code ...
I made a plugin for jQuery, which I think is quite useful. It combines an animated colours plugin with an easings plugin, and adds a completely new feature of being able to refer to colours ...
The question jQuery plugin file including the jQuery library came up today on stackoverflow, and I strongly advised against including jQuery in the plugin. I didn't really get any support from others ...