Y.Kohno

This is a flexible search form widget. 
You can easily generate a multi condition search form and display anywhere as widget.
複数のカスタムフィールド、投稿タイプ、カテゴリー、タグでの検索が可能な複合検索フォームを簡単作成できるプラグイン。ウィジェットで好きな場所に設置可能。
Currently supports 
– Custom Fields 
– Taxonomies 
– Categories 
– Post tags 
– Post Type

WP Meta Search

Search form for searching through custom fields, post types, categories, tags, and free text.

Ben Balter

This plugin will work, “as is”, out of the box, but assumes some level of CSS and developer customization to adapt to your site’s specific needs.
Styles can be overridden via your theme’s style.css
Functionality can be overridden via your theme’s functions.php
”Examples”
Don’t display metabox on “product” post type:
<pre><code>add_filter( 'display_custom_fields', 'bb_no_product_metabox' ); function bb_no_product_metabox( $true, $post ) { if ( $post->post_type == 'product' ) return false; return true; } </code></pre>
Don’t display the product_id metakey
<pre><code>add_filter( 'dcf_postmeta', 'bb_no_product_id' ); function bb_no_product_id( $postmeta ) { unset( $postmeta['product_id'] ); return $postmeta; } </code></pre>
Don’t display metabox title
<pre><code>add_filter( 'dcf_heading', '__return_false' ); </code></pre>
Display metabox below content (rather than floated to the right)
<pre><code>add_filter( 'dcf_before_content', '__return_false' ); </code></pre>

Display Custom Fields

Inserts a Wikipedia-like metabox into posts with all the post's associated custom fields and taxonomy terms.

WP Meta Search vs Display Custom Fields