(all are working with WP v3.5.1)

Cost: Free

  • Auto-schedule Posts by David Miller - Queue your posts to roll out over the course of the day.  Update: I decided I don't need this, and haven't checked this out since WP 3.4.2
  • Auto Save Remote Image by Prebhdev Singh - WP doesn't handle remote linked images very well. First, the links might be broken.  Second, the Featured Image option (ie post thumbnails) only work with local images.  Prebhdev's plugin fetches the remote images and saves a local copy, then sets the Featured Image and all other references to the local one.  Update: This hasn't been updated in a while.  I just got used to uploading images to my site, so remote images are no longer a priority.
  • HTML Javascript Adder by Aakash Chakravarthy - as the author says, it allows you to insert HTML, javascripts, shortcodes, advertisements, flash embed codes, and plain text as a sidebar widget.  I use it to post my customized FB button and Google Analytics tracker.
  • IFRAME by  webvitaly - Insert the {iframe} shortcode in your pages to embed other pages or elements such as Youtube, Vimeo, or Google Maps.
  • Jetpack by Wordpress - Gives you many of the features enjoyed by Wordpress.com hosted blogs.  Gain a social commenting system,  stats, URL shortener, social sharing buttons and auto-posting, spell check, contact forms, and automatic reformatting of your site for mobile devices.
  • Nextgen Gallery by Photocrati - WP's media organization is somewhat lacking. This lets you organize your images into galleries and then insert them as galleries or slideshows using a simple shortcode.  There are a variety of plugins that build upon the Nextgen framework.  I'm not a fan of the interface (a little archaic) but it can be useful. (The gallery management is inferior to WP3.5's built-in).
  • Subscribe2 by MattyRob, Skippy, and RavanH.  This Wordpress plugin provides viewers the ability to receive your posts by email.  This is great for keeping mom, dad, and the other greyhairs in the loop, since they might not have or might not like to use the social networking sites like Facebook.  I tried to get by with the integrated Jetpack subscriptions but it had several deficiencies: 1) Inability to edit the subscription list, 2) Emails complete posts, meaning the readers never need to visit your site.  Subscribe2 gives you the ability to manually add addresses (making it possible to automatically repost to Posterous, Blogger, Wordpress, etc using their Post by Email features (you can't do this with Jetpack since it requires a confirmation reply that those sites will never send).  Subscribe2 also lets you customize the emails in several ways: send out individual articles or daily/weekly/monthly digests; post excerpts or full articles; filter certain categories.  Comes with its own widget, too.  The only downside I can see is that support might some day evaporate.  But for now it's a hit.
  • Wunderslider by itthinx - Can be used to enhance your Nextgen slideshows.  Flash-less (yay!) Pretty customizable although I don't think it's worth the donation price (poor documentation).  The homepage slideshow uses this.  Has problems resizing for smaller screens, unfortunately, which is why I'm looking for a mobile-friendly alternative.
  • Wordpress Backup to Dropbox by Michael de Wildt - Copies the contents of my server to my dropbox on a daily schedule.  Your SQL databases are there too.  Saves a lot of headache.
  • WordPress Media Tags by Philipp Speck - Tag your media files because that's pretty much the only way you'll be able to search for them.  I can't believe WP doesn't provide media tagging by default, nor a good way to organize your media into folders.  It becomes a pain once your media library grows.
  • WPtouchPro by Brave New Code - The Jetpack 2.0 release gives automatic reformatting of your site for mobile devices, but doesn't offer much customization.  WPtouch (free) and WPtouch Pro (licenses from $49, this is what I use) give you almost total control.
  • WP Super Cache by Donncha O Caoimh - This is the only one I WOULD NOT completely recommend. However it's the lesser of two evils, as W3 Total Caching Plugin is an even worse monster. Anyway, I don't know why WP Super Cache was installed for me by default.  It A) prevented me from seeing the results of my site modifications because it doesn't know how to say "oh, you've modified that page, let me refresh the cache", and B) it doesn't remember its own settings (change an option and you'll find it doesn't take, as well as other options mysteriously enabled/disabled.