I have been recommending a lot of plugins and experimenting a lot myself. I will revise here some of good WP-Plugins which I have found quite useful.
Whenever a post is viewed, WordPress compiles all the code together and transforms code into single page with post(s). When a blog gets hundreds or thousands of hits per day then most probably your hosting server will be gone if you are at small server. WP-Cache is an extremely efficient WordPress page caching system to make you site much faster and responsive. It works by caching Worpress pages and storing them in a static file for serving future requests directly from the file rather than loading and compiling the whole PHP code and the building the page from the database. WP-Cache allows to serve hundreds of times more pages per second, and to reduce the response time from several tenths of seconds to less than a millisecond. A must have plugin. You can set caching expiry time and other all options from admin.
Download WP-Cache WP Plugin
Social BookMarks 4
I have earlier mentioned this one here. This plugin had an issue of sending 404. I requested dountsis for an update. In 24 hours he updated the plugin and now its bug fixed and great plugin for using 50 popular bookmarking services with your blog.
Download Social Bookmarks 4
If you will not bother about 404 hitting your blog then your server will create a log file containing 404 errors. It is ‘page cannot be found error’. I was horrified to see 404 errors long list from server log. Then I took this plugin seriously. Because if your blog is hitting 404, it means more burden upon server, users rate reduction, reduction in blog functionality and more then you can imagine.
404 can be due to typo or because of any plugin usage. What 404 does is, it notifies you via email about referring URL and also the 404 URL so that you can fix it. For SEO point of view and also for health and growth of your website or blog there must be no 404.
AddThis Social Bookmarking Widget (drop-down)
Another great social bookmarking plugin. Sleek and wonderful. Pluggable with any blog, any website and highly customizable. I will suggest you its drop-down version to use. AddThis features easy sharing, easy bookmarking, spreads your content, increases rankings, removes clutter, easy to install, free statistics, and reliable.
Optimal Title Plugin
SEO part for your blog. Modify default title for your blog. This will modify meta part and let you customize title. This allows you to have your blog name tacked on to the end of the page title instead of having it appear first. Having your page information appear before your blog name in the title is advantageous because it provides more meaningful search engine results and browser bookmark names.
Download Optimal Title Plugin
SRG Clean Archives (sitemap)
Have a sitemap for your blog I would say. Ajax based clean sitemap storing all archives and posts of your website. Any post just two clicks away with this plugin. This plugin is designed to display your archive listings in a clean and uniform fashion that’s Search Engine friendly on a dedicated page or in your sidebar. Great one. View Clean Archives Demo.
Download Clean Archives