1. ColorpickerColorpicker in jQueryUI style. Themeroller look & feel. Multiple color spaces, input/output formats, controls. Check the demo...
2. CoverflowYet another jQuery Coverflow widget. Support for mousehweel, touch, reflections and complex CSS animation. Events for pretty much everything. Controllable using various methods. Options to change pretty much everything, but works fine without any options.
3. PhpsyllablePHP Syllable splitter/counter and Hyphenator for text and HTML. Multi-language, customisable, cached and fast!
4. tristatejQuery standalone tristate (indeterminate) checkbox with pseudo selectors and optional value modification and .val() overwrite. Standalone, so usable for purposes other than list/tree marking.
5. limitsliderjQuery slider extension forcing gaps and order for any number of handles.