There are thousands of WordPress plugins out there. What follows is a list of plugins with which I have personally had good experiences:

  • Broken Links -- Broken Link Checker automatically checks and reports broken links.
  • To Do List -- Cleaverness To-Do List enables you to keep track of what you have to do. CAn be used for just about anything but I use it to keep track of what needs to be done on a website.
  • Constant Contact API and Contant Contact API: Form Designer -- only useful if you use the Constant Contact service. Note that these do not integrate with s2Member.
  • Contact form – Contact Form 7 allows you to create forms on your website. Others may be easier to use but this one includes a very complete set of features. Check out Contact Form 7 Modules: Hidden Fields and Contact Form 7 Send All Fields too.
  • Easily Clone/Duplicate Posts and Pages -- Duplicate Posts plugin. I could write a whole article on the value of this plugin alone to measure the performance of marketing campaigns.
  • Performance Optimization: P3 (Plugin Performance Profiler) helps you determine what is slowing down your WordPress site. W3 Total Cache OR WP Super Cache will speed up your website by caching the content as static pages whenever possible.
  • Development Tools: , Lorem shortcode helps you create sample image and text content while developing a new site. Simple Page Ordering enables you to easily sort pages.
  • Related Links for blog posts -- ELI’s Related Posts Footer links and Widget
  • Exclude Page from Navitation -- Exclude Pages gives you the option to exclude certain pages, such as your sites the Privacy Policy, a search page or a thank you page, so that it doesn't show up in the the navigation menu.
  • Feedburner: FeedBurner FeedSmith Extended allows you to easily make use of Google's FeedBurner service to manage RSS subscriptions to your site.
  • Analytics: Google Analiticator -- Show WordPress Stats from Google Analytics right in your dashboard. Social Metrics help you keep track of page specific “Likes” on social media sites.
  • Security: Limit Login Attempts prevents people from getting lucky when trying to break into your website by limiting the number of bad username/password attempts before it disables your website. AntiVirus helps by ensuring you don't inadvertently install a plugin that contain a virus. Akismet Anti-Spam will do a very good job of filtering out spam comments in response to your posts and pages.
  • Settings: Page Comments Off Please sets the comments setting off for pages by default so that you don't have to always remember.
  • Menu links to non-wordpress URLs: Page Link To enables you to create menu links to other websites and files on your site.
  • Create multi-level Membership and Subscription areas and Shopping Carts using s2Member Framework
  • SEO: WordPress SEO by Yoast plugin (or All in one SEO Pack). I prefer WordPress SEO because it integrates links to other useful SEO tools. Not only will it generate XML site maps but it will notify the major search engines when you make a change to your site. If you end up going with All in one SEO pack, be sure to add the Google XML Sitemaps plugin too.
  • Content Slider: TheThe Image Slider
  • Wordprocessor-like WYSIWYG editor -- TinyMCE editor : Ultimate TinyMCE adds functionality to the WordPress WYSIWYG editor. TinyMCE Templates gives you the ability to create reusable content templates. TinyMCE Signature is great if you tend to always sign your blog posts the same way.
  • Be able to work on the website while displaying a message for people who are not logged in: Ultimate Coming Soon Page
  • Ability to upload files: WP File Manager is really useful for transfering and editing files, especially if you don't have FTP access.
  • Backups: XCloner backs up both all the files and the database content.
  • Support for mobile devices: WPTouch, Wapple Architect or WordPress Mobile Pack
  • Autoresponder: WP Autoresponder and WP Autoresponder to s2member Integration
  • PayPal Enabled Shopping Cart: WP Simple Paypal Shopping Cart / UI for WP Simple Paypal Shopping Cart
  • Embed a video in your page – Contrary to popular belief, you don't need a plugin to do this. It can be as simple as just pasting in a YouTube URL. If that doesn't work, just put an embed shortcode tag around the URL. Example: http://urltoyourYouTubeVideo
  • Polls – WP-Polls