WordPress is the most populor blogging plantform.Not only small blog use the free open source wordress, but the huge sites also use wordpress as thier CMS.There are a lot of free wordpress plugins, with these you can make your website more powerful and useful,and maneage your sites more easily.Here is a collect for the more populor and useful wordpress plugins for you.

• All in One SEO Pack – WordPress Search Engine Optimization plugin
  Most of the blogs are using this powerful Search Engine Optimization plugin.Optimizes your WordPress blog for Search Engines like google, yahoo,live etc. This wordpress plugin will make the search engines “understand” your ariticles more, this may get more free traffic to your blog.Besides,  you should properly create, configure, and optimize Google XML Sitemaps.xml, sitemap.xml.gz, and robots.txt etc.
• WP Super Cache -Make your blogs run faster
  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.If you use this plugin, your blog hosting will run more faster.And I know anthoer super wordpress cache, which generates REALL static html files(cos-html-cache )! You can find those files on your server! If you use WP Super Cache , when the  mysql server can not work anymore, your websites can’t open; but if you use cos-html-cache, visitors still can visit your website even the myqsl hosting crashdown.
• Faster Image Insert-Upload multiple images one time
  Integrates media manager into edit panel, avoid having to reload it separately in thickbox, suitable for magazine-style blog post control.I love this wordpress picture plugin, make me upload images more easily.
• WP-PageNavi – More easy to visit your website
  Adds a more advanced paging navigation to your WordPress blog.After you have installed this plugin, the paging navigation will like this , there ar eno next or previous anymore.More easy to access.
• WordPress Database Backup- Back up your blogs and let your datas safe
  WP-DB-Backup allows you easily to backup your core WordPress database tables. You may also backup other tables in the same database.You can backup your database ontime, and make a schedule , then it will send your backup datas to your email.
• WP-SpamFree -Stop Spam comments
  An extremely powerful anti-spam plugin for WordPress that virtually eliminates comment spam, including trackback and pingback spam. Finally, you can enjoy a spam-free WordPress blog! Includes spam-free contact form feature as well. A Powerful Weapon Against Comment Spam Comment spam has been a huge problem for bloggers since the inception of blogs, and it just doesn’t seem to go away. The worst kind, and most prolific, is automated spam that comes from bots.
• Contact Form 7 – Add  forms to your sites.
  Just another contact form plugin. Simple but flexible. Contact Form 7 can manage multiple contact forms, plus you can customize the form and the mail contents flexibly with simple markup. The form supports Ajax-powered submitting, CAPTCHA, Akismet spam filtering and so on.
• WordPress Add to Any Share/Save/Bookmark Button– Social websites links, get more traffic.
  Helps readers share, save, bookmark, and email your posts and pages using any service, such as Delicious, Digg, Facebook, Twitter, and over 100 more social bookmarking and sharing sites. The button comes with Add to Any’s customizable Smart Menu, which places the services visitors use at the top of the menu, based on each visitor’s browsing history. The E-mail tab makes it easy to share via Gmail, Y! Mail, Hotmail, AOL, and any other web-based e-mailer or desktop program. The Bookmark or Add to Favorites tab helps users bookmark using any browser (Internet Explorer, Firefox, Chrome, Safari, Opera etc.). Individual service icons let you optimize your blog posts for specific social destinations.
• WP e-Commerce -Sell your products online
  The WP e-Commerce shopping cart plugin for WordPress is an elegant easy to use fully featured shopping cart application suitable for selling your products, services, and or fees online. WP e-Commerce is a Web 2.0 application designed with usability, aesthetics, and presentation in mind. Perfect for: Bands & Record Labels Clothing Companies Crafters & Artists Books, DVDs & MP3 files