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.

karevn

This plugin adds simple HTML tag generation API to WordPress, like these examples: 
 generates and prints <code><img src="/wp-content/<your-theme>/images/wordpress.png" alt="Wordpress" /></code>. 
 ‘my-image’)) ?> generates and returns almost the same tag, just with absolute url, id and alt attributes set manually. 
 term_id) ?> generates select tag with options taken from WP ‘category’ taxonomy and sets $term as selected item 
 rails-like “cycle” that returns “odd” on first call, “even” on second, “odd” on 
 third call, so on. reset_cycle resets the cycle. 
 shortcut for echo(get_post_meta($id, ‘meta_name’, true))
Form field generators for <code>text</code>, <code>checkbox</code>, <code>hidden</code> input types, <code>textarea</code>, and more tags. More docs coming soon, you can read the code to figure out other features for now.

HTML Helpers

This plugin adds simple HTML tag generation API to WordPress.

Safe PHP Code Widget vs HTML Helpers