Share and Follow Plug In. Andrew Killen
mighty W3 Total cache:
CryptX: If you need to have an email address on the page, but really HATE spam, this plugin will do a little java script for you.
Uber Login Logo: Change login logo. If you want to do more customization, then you’ll need to do a little programming, but this is an nice quick fix. by UberWeb
Advanced Custom Fields. Custom fields have come a long way, but Advanced custom fields makes it easy to customize your theme so users can easily update their sites from one page and not have to always use widgets. By Elliot Condon
Mail From: Change the default address that WordPress sends it’s email from. By Andrew Hamilton
Under Construction: Makes it so your site can only be accessed by users who log in. Useful for developing a site on a live server, without the world being able to see it. by Jeremy Massel
Revisionary: Enables qualified users to submit changes to currently published posts or pages. These changes, if approved by an Editor, can be published immediately or scheduled for future publication. by Kevin Behrens
Role Scoper: CMS-like permissions for reading and editing. Content-specific restrictions and roles supplement/override WordPress roles. User groups optional. This one goes with Revisionary and is also by Kevin Behrens
User Role Editor It allows you to change any standard WordPress user roles (except administrator) capabilities list with a few clicks.
Contact Form 7: Just another contact form plugin. Simple but flexible.
Contact Form to DB Extension: Save form submissions to the database from Contact Form 7 and Fast Secure Contact Form. Includes exports and short codes.
WP Better Security: Better WP Security takes the best WordPress security features and techniques and combines them in a single plugin thereby ensuring that as many security holes as possible are patched without having to worry about conflicting features or the possibility of missing anything on your site.
meta Tag Manager: Meta tags are really a thing of the past, but many clients still demand them, and they can’t really hurt your results, so if you must, add them, this is a very easy solution, and it allows your client to update them, too. More WP meta tag information.
A good list from 2009