Staple Wordpress Plugins for Any Website
Here's a look at Wordpress plugins that I use for pretty much any website I build for a client. For most intermediate users you're probably accustomed to seeing/using these plugins, but I hope this will become a good resource for someone starting out!
Magic Fields
This is the holy grail for any WP site that needs custom post types or custom fields with a nice UI for you and for the client. There's a lot of documentation out there for using this as well on a misc. sites and they also have their own site as well here. There are 2 versions out, both of which are helpful depending on what you're trying to do.
Password Protect Plugin for Wordpress
This is useful for when you need to password protect the whole site if you're in the middle of building a WP website. Simple and gets the job done. You just activate and done!
Regenerate Thumbnails
If you change the resize dimensions to your images and you're wondering why your images aren't updating it's probably because you need to regenerate them and this plugin does that! I would suggest uploading a few images to test out your image sizes and then regenerate thumbnails to fix any sizes so that you're not waiting to regenerate over 100 photos you uploaded without making sure the resized images looked okay beforehand.
Contact 7
This is probably the most flexible contact form that I've come across. I don't think it has the best UI but for more custom solutions where your client needs to be able to add/edit the fields or create new forms this can come in handy. It is also AJAX form submit which is nice, especially if you have a form in a modal window and would rather not have it redirect to a thank you page. You can also gather all of the data sent with these form into a database by installing this extension.
WP Super Cache
Pretty much self explanatory, I've never had a problem with this plugin when I need to cache the pages on the website. Just remember if something isn't updating on your site Clear the cache!!
WordPress SEO by Yoast
This is great for adding SEO customizations for your clients (or you) to control. I like the advanced tab as well where you can control and specify a post type/page/post 'noindex' for pages you don't want to show up in search engines.
Let us know in the comments of any plugins you use for any WP website you build!