Akismet. It protects your blog and website for spam comments. I receive over 1000 spam comments every day on my few blogs that I manage. It comes by default with WordPress so only you have to do is to activate it trough your administration panel.
Yet another related posts plugin. Almost wll blogs use it. At the end of every article it will show a list with 3 or more related post. It will give to every 2 articles a match score by analyzing the content. From the admin panel you can select the minimum match thereshold that you should display as your related posts. To get always the highest number of related posts set that thereshold as 1.
Contact form. It is a must to provide your visitors with a way that they can contact you. Posting your e-mail address on a page will get it spidered by robots and then you will get thousand of spam emails every day. In WordPress, to show a contact form you have just to install a plugin and paste a code in a new page that you create trough WordPress page editor.
SEO plugin. All website needs SEO. No to exploit the search engines, but to try to provide the best value to the search engine visitors. Having a SEO plugin don’t assure you top rankings on high traffic terms, but will show your posts when people search for them.
About the author box. Your readors want to know who are you. With a simple plugin you can add your info and your photo to the end of every article.
Sociable is a social bookmarking plugin. At the end of every post it will show links that goes directly to the bookmarking page of different social bookmarking or social networks. If someone likes your post it will want to share it with his friends. Give him the option to share it on Digg, Twitter, Facebook and other 100 available networks. Don’t show them all, select which to appear.
Lightbox plugin will add a new functionality in the way image are viewed on your blog. By default, when a visitor click on an image, it will be send to a new page and the image opens. Lightbox will open the image as an in-page pop-up and the rest of the website will have a shadow on it. This is why it is called lightbox: when the rest of the website is shaded, the picture seems to have lights on it.
Freebie images is a plugin that will search automatically for free stock photos based on your post content. In this way you can show a descriptive image about every post in your blog.
Feedburner plugin. If people like your articles they will want to receive them on email or to read in their favourite blog reader software. To provide the best functionality for this you have to setup a feedburner account. For best behaviour install feedburner feedsmith plugin.
Wp-polls. Use this to add polls in your pages or blog posts. It is simple to use: create the poll and show it to any page you want by adding a short code