usefull plug-in

I’ve used these lovely plug-in of WordPress in my wordpress box an they work as expected

WordPress Widgets:

This is probably the first plugin you’ll want to grab. It allows you to easily arrange the contents of your sidebar. There are also tons of great “sidebar widget” plugins available.
SEO Title Tag:

One of the most important plugins for (SEO) search engine optimization. It allows you to reverse the WordPress blog name and title to show better keyword prominence.

Google Sitemap Generator:

Automatically generates Google Sitemaps for your Blog.

WP Cache Plugin:

As you start to build traffic to your blog, you’ll soon experience a need to reduce the load on your server. The WPCache plugin for WordPress alows you to serve many more pages per second. It does this by caching each page to the server upon the first load of the page so the page doesn’t have to be compiled the next time it is served.

And below are recommended plug-in i might install in the future

WP Contact Form:

Allows people to contact you via a submission form. This means that you don’t have to expose your e-mail address anymore.

WP Database Manager:

This magnificent tool allows you to manage your SQL database directly from within WordPress.

WP E-Mail:

Enable your visitors to send an E-Mail of the post directly to their friends.