Let's just start out with one important note - Keep It Simple - While there are thousands of components and modules available to you for your
Joomla website resist the urge to install everything at once. Get comfortable managing your new site before you start adding bells and whistles.
That being said here is a short list of add ons that I have been using on every recently built Joomla site.
In no particular order:
Add to Menu is an Administrator module. You will get an extra link in the top right of your Administrator to quickly add a menu item link of the page you are viewing.
As the reviews state: A simple TIMESAVER
JCE - An award-winning, configurable WYSIWYG editor for Joomla! based on Moxiecode's TinyMCE.
Includes advanced Image/Media, File and Link handling, plugin support, and an Administration interface for editor configuration.
Grab the media box plugin for it too!
Simple Content Versioning - This component and two plugins provide a simple content versioning solution for Joomla. It saves a backup copy each time content is saved. It also adds an editor button to allow you to restore a document you're editing with a backup version.

FBoxBot is a joomla bot/plugin. The main idea is to help the user to create easily thumbnails from any pictures, and when you click on the thumbnails a nice "lighbox-like" popup appears that show the image at its original size. Disable lightbox with the following code as the class in the JCE editor:
nofb="nofb" width="70">
swMenuFree - Create a dynamic popout or dropdown menu module for your site!
XIJC Captcha Component - Essential spam blockingfor all Joomla powered websites!