Akismet
It’s great for stopping spam and works really well without having to annoy your commentors with unreadable CAPTCHAs.

All-in-one SEO Pack
All-in-one SEO pack is a must have plugin for any website or blog. While it works perfectly out of the box, you can also fine-tune any of its settings if you wish. It works by giving you a unique title and meta tags for each page and post. You can even give it your own meta info from each post page.

Contact Form 7
Completely configurable and easy to set up.

Google XML Sitemaps
Google XML Sitemaps automatically creates a new sitemap and submits it to major search engines every time you add a new page or post to your site.

Page Links To
One page thing about using WordPress’s built in navigation function, or wp_list_pages(), is that you can’t add extra links in (unless you want to add them before or after the function). Page Links To solves this problem by allowing you to create a WordPress page and then telling it where to actually link to. It works with any link on or off the server.

Socialize This
Socialize This is almost 3 plugins in 1. The main function of this plugin is to put share links on the bottom of your post. It allows you to choose the icon set, which sites to use and what order to put them in. However, you can also set this plugin to send a tweet to your account when a new post is published and it provides short URLs for all your posts.

Twitter for WordPress
Twitter for WordPress is a plugin that simply displays your latest tweets anywhere on the site. You can use their widget or you can place it anywhere in your theme with their function call.

SNV Facebook Like Button
SNV Facebook Like Button puts a pretty button on the bottom of posts that allows the user to “Like”, which sends the article to their Facebook page, and displays which friends of the user have already liked the post.

Simple WordPress Backup
Simple WordPress Backup allows you to back up your WordPress Database with just one click.
Creates a full dump of your WordPress MySQL Database.

Google Analytics for WordPress
This plugin makes it simple to add Google Analytics to your WordPress blog, adding lots of features, eg. custom variables and automatic clickout and download tracking.

Premise
Quickly and easily create amazing landing pages for your WordPress site.

HeadSpace2
Meta-data manager on steroids, allowing complete control over all SEO needs such as keywords/tags, titles, description, stylesheets, and many many other goodies.