There are plenty of plugin available for WordPress blog. There are must have plugin and some for different use of blogging.

WordPress is a powerful blogging platform and there are many powerful plugins that increase power of WordPress. Some plugins impact on frontend like displaying ads; sidebar widgets etc but there are many plugin which do not impact frontend but make your blog powerful from backend and make you keep relax.

7 Powerful Backend Plugins

All in One SEO Pack: Optimizes your Wordpress blog for Search Engines Automatically optimizes your titles for search engines, Generates META tags automatically, Avoids the typical duplicate content found on Wordpress blogs You can override any title and set any META description and any META keywords you want. You can fine-tune everything. Backward-Compatibility with many other plugins, like Auto Meta, Ultimate Tag Warrior and others.

This plugin will help you to make your blog more search engine friendly.

Google XML Sitemaps: This plugin will create a Google sitemaps compliant XML-Sitemap of your WordPress blog. It supports all of the WordPress generated pages as well as custom ones. Every time you edit or create a post, your sitemap is updated and all major search engines that support the sitemap protocol, like ASK.com, Google, MSN Search and YAHOO, are notified about the update.
This will help search engines to find your blog post more quickly.

Google Analytics for WordPress:  The Google Analytics for WordPress plugin automatically tracks and segments all outbound links from within posts, comment author links, links within comments, blogroll links and downloads. It also allows you to track AdSense clicks, add extra search engines, track image search queries and it will even work together with Urchin.

Google Analytics is a free site monitoring service. This plugin will help you add Google Analytics to your blog. With the reports you will get lot of help to improve your blog.

Align RSS Images: Align RSS Images is a simple plugin that scans your RSS feed and ensures that every image has the correct alignment and margin settings. This is useful if you want the images to appear correctly aligned not just on your site, but also in your RSS feed.

StatPress Reloaded: This plugin (previously known as StatPress) shows you real time statistics about your blog. It collects information about visitors, spiders, search keywords, feeds, browsers, OS etc

WP-DB-Backup: WP-DB-Backup allows you easily to backup your core WordPress database tables. You may also backup other tables in the same database.

WP Super Cache:  This plugin generates static html files from your dynamic WordPress blog. After a html file is generated your webserver will serve that file instead of processing the comparatively heavier and more expensive WordPress PHP scripts.