WordPress Plugins

Security

Better WP Security – http://wordpress.org/plugins/better-wp-security

Wordfence – http://wordpress.org/plugins/wordfence/

Sucuri – http://sucuri.net

Vaultpress – http://wordpress.org/plugins/vaultpress/

Backups

Vaultpress – http://wordpress.org/plugins/vaultpress/

BackupBuddy – http://ithemes.com/purchase/backupbuddy/

Functionality

Jetpack – http://jetpack.me – remember that unless you need a large amount of Jetpack’s functionality there are likely to be stand alone plugins that manage things as easily without the server overhead.

Management Tools

Command Line Interface – http://wp-cli.org/

Infinite WP – http://infinitewp.com/

W3C Code Validation – http://validator.w3.org/

Akismet Spam Manager – http://akismet.com/

Contact Forms

The industry standard plugin for creating awesome forms, not just for contact pages, but any kind of site data gathering is Gravity Forms. The functionality of this (premium) plugin is pretty extensive and worth every penny.

Gravity Forms – http://www.gravityforms.com/

JetPack – has a contact form, see link above

Contact Form 7 – http://wordpress.org/plugins/contact-form-7/

Fast Secure Contact Form – http://wordpress.org/plugins/si-contact-form/

SEO

Great tools for optimizing content for search engines

WordPress SEO by Yoast – http://wordpress.org/plugins/wordpress-seo/

All in One SEO – http://wordpress.org/plugins/all-in-one-seo-pack/

Site Speed & Efficiency

These first three create static versions of your pages to make serving files a lot quicker… less db calls

WP Super Cache – http://wordpress.org/plugins/wp-super-cache/

WP Hyper Cache – http://wordpress.org/plugins/hyper-cache/

W3 Total Cache – http://wordpress.org/plugins/w3-total-cache/ This is an awesome plugin, does lots to improve site load, but can be really tricksy to get right… backup first

WP Minify – http://wordpress.org/plugins/wp-minify – This one concatenates your scripts so that you reduce http calls… also speeds things up