captbrogers

An anti-spam captcha using jQuery’s UI slider. After the position of the slider is past 60% (default), it will enable the submit button. This will replace the input button specified as the submit button, if JavaScript is not enabled the button will show as expected.

WP Slider Captcha

An anti-spam captcha using jQuery's UI slider. After the position of the slider is past 60% (default), it will enable the submit button.

Rafiki

Allows for front-end tagging of posts. It uses jQuery UI autocomplete to search the WP DB 
and return the closest matching tag based on the search term. If no tag was found, 
you can add a new tag by simply hitting the enter key.

QuickTags

Allows for front-end tagging of posts via a simple widget.

WP Slider Captcha vs QuickTags