k0tik

The usual Text widget allows you to insert arbitrary Text and/or HTML code. This allows that too, but also parses any PHP or JavaScript code in the text widget and executes it.
This plugin is based on “PHP Code Widget”, but now available for use by site administrators ONLY, which makes it more secure.
All PHP code must be enclosed in the standard php opening and closing tags ( <code><?php</code> and <code>?></code> ) for it to be recognized and executed. Also JavaScript code must be enclosed in the <code><script></code> and <code></script></code> tags, as usual.

Safe PHP Code Widget

Adds a secure and simple widget in which you can use PHP and JavaScript code. Also you can use unfiltered HTML or just Text. Admin Use Only.

RMWebsec

Like a normal text widget this allows you to easily post text and HTML, but 
now you can execute PHP too! 
This makes merging with other themes easier.
!IMPORTANT! You must use tags for the code to be 
recognized.

PHP-Widgetify

Execute HTML, Text or PHP fast and easy with this Widgetify-widget.

Safe PHP Code Widget vs PHP-Widgetify