I recently developed an online template builder (www.jstemplates.com) for which I used quite some JQuery modules.
I used the JQuery UI accordions, slider, buttons and dialog. I also used the superfish menus and spectrum, a colorpicker.
I would never have been able to build this thing in only 3 weeks without the power of JQuery.
Thanks to all developers making this JQuery framework an excellent starting point for web developments. I believe JQuery should be built-in into browsers :)
Give www.jstemplates.com a try please! (it's free of course!)