1	Aksimet	Akismet checks your comments against the Akismet web service to see if they look like spam or not.
2	Google XML Sitemap	This plugin will generate a special XML sitemap which will help search engines like Google, Yahoo, Bing and Ask.com to better index your blog.
3	All in one SEO Pack	Out-of-the-box SEO for your Wordpress blog.
4	WP-Optimize	This plugin helps you to keep your database clean by removing post revisions and spams in a blaze. allows you to rename your admin name also. Additionally it allows you to run optimize command on your wordpress core tables (use with caution).
5	Google Analytics for Wordpress	This plugin makes it simple to add Google Analytics with extra search engines and automatic clickout and download tracking to your WordPress blog.
6	WP-Cache	Very fast cache module. It’s composed of several modules, this plugin can configure and manage the whole system.