jQuery multiselect drop down menu

Answer 1

Update (2017): The following two libraries have now become the most common drop-down libraries used with Javascript. While they are jQuery-native, they have been customized to work with everything from AngularJS 1.x to having custom CSS for Bootstrap. (Chosen JS, the original answer here, seems to have dropped to #3 in popularity.)

• Select2: https://select2.github.io/
• Selectize: http://selectize.github.io/selectize.js/

Obligatory screenshots below.

Select2:

Selectize:

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Original answer (2012): I think that the Chosen library might also be useful. Its available in jQuery, Prototype and MooTools versions.

Attached is a screenshot of how the multi-select functionality looks in Chosen.