Ajax Search Pro for WordPress was designed to boost the user search experience to the maximum. It provides a live ajax search, which makes the wordpress search experience more confortable. The results are presented with images (if any found), so they look more attractive and less flat.
Features

400+ possible options on admin panel
70+ pre-defined fully customisable themes
Vertical / Horizontal / Polaroid and Isotopic styled results list
Multiple search plugins on one page – You can configure all of them separately!
Google Keyword Suggestions on no results, witch a ****** selector
Responsive width
Search caching & image precaching for better performace
Search in public custom fields is now possible!
2 New widgets: Latest searched keywords and Top searched keywords! – You can setup a sidebar widget of the latest/top used keywords and even trigger a search by clicking on them!
Results filtering by: categories, terms, tags, custom fields, date
Search relevance options with adjustable weight values
Retina ready SVG icons
WPML support
Polylang support
qTranslate(x) support
Dynamic string translations via Polylang or WPML string translations
.pot file included for a fully translatable Admin Section
Google Analytics Integration module
Scroll-to-results option
Keyboard navigation for vertical results
Multiple instances of search boxes are now possible
Better preview
Shortcode buttons on the Post editor
Better image options and image handling
Hooks – Filters & Actions for developers
For the full list see the changelog down below!
Search statistics page
Default search text
Intelligent image parsing (possible from post featured image, post content, post excerpt, possible to set priorities as well)
Custom Post Types support – You can select which post types do you want to search! Tested with BBPress!
Font, color, border, box shadow options
Keyword Highlighting in search results
Works in templates and in post and pages as well
Search widget also included
Preview window on the admin page
Mobile support
Frontend Search options popup
Possible to search in Posts, Pages and Products (WooCommerce, Jigoshop, WP-ecommerce etc..)
Image caching for bandwidth saving
Very easy installation and set up
Powerful api for controlling the search from other frontend applications
jQuery powered, for the best possible compatibility
Show more results link below the search box
WordPress 3.5+ compatibility!
Multisite support!
Search autocomplete with search statistics or google keywords!
Error checking module
Shortcodes can be executed in search results
Search result content HTML tag stripping is possible
Category selectors on the frontend – It’s possible to filter the posts by categories
You can select custom fields as post title and description
Post grouping by category or post type!
Search in comments
It’s possible to exclude categories or posts from the search!
Stable, custom built jQuery for maximum compatibility
Shortcodes strippable/executable in results
Supports pages with categories/taxonomies
PeepSo Groups & Group activities search
Index table search capabilities:
Indexing titles, content, exceprt, authors, custom fields, categoires, tags etc…
Indexing shortcodes content
Compatible with PODs – including indexing PODs custom table meta fields
Compatible Advanced Custom Fields (ACF) plugin’s:
Text field
Textarea field
Date field
Number field
Email field
WYSIWYG editor field