The WordPress blog platform has thousands of plugins, and many of them now use ajax to improve usability. Pete Cashmore, has compiled a list of more than 30 AJAX plugins into two categories, for the blogger, and for the reader which includes:
For the blogger:
AjaxWP - Adds AJAX to all aspects of your WordPress site speeding up the load times.
Alexa Rank - Display your Alexa rank with pride.
Ajax Comment Preview - Allows readers to preview their comment before submitting.
asTunes - Retrieves data from your Audioscrobbler/last.fm profile and posts it as a list on your blog.
Codebox - Side scrolling box for displaying code snippets.
Crossroads - Adds thumbnails and comments from your Flickr account.
FireStats - Full featured statistics including referrers and popular pages.
Google PageRank - Allows you to display your Google Page rank on your blog.
Hardened-Trackback - Generates a single use trackback to help fight trackback spam.
imgViewJX - Refreshes an image on your main page from a selected directory.
Live Spell Checker - Adds a spell checker to the admin area to check your posts with.
Plug ‘n’ Play Google Map - Adds any post you make with longitude and latitude to a Google Map on a separate page. Very useful for blogs writing restaurant reviews or about events.
WordPress Mailing List - Have a mailing list? Let readers subscribe and unsubscribe simply from the front page of your site.
WP e-Commerce - Adds a shopping cart to your WordPress powered site.
WP-Polls - Adds fully customizable polls for your readers to take.
WP-Post Ratings - Allows readers to rate your posts.
Zorpia That’s Hot Box - Allows visitors to send posts they like Zorpia.com and vote on their favorite articles.
For your readers
AJAX Comments 2.0 - Auto updates the comments page with no full reload, much smoother commenting than the older full reload system.
AJAX Google Video Search - Search Google Video without having to leave your favorite blog.
AJAX Shoutbox - Realtime conversation with sound to alert of new messages.
Cool Weather - Allows visitors to see the weather forecast for any area they define.
Currency Converter - Adds a real time currency converter to the page with data pulled from Yahoo Finance.
Google AJAX Search - Allows you to set search for just the contents of your site and the web, or another option allows for search of a second site such as your Flickr account.
Google MapSearch Widget - Allows readers to search Google Maps without ever leaving the page.
Gregarious - Social bookmarking plugin that adds Digg, Reddit, Feedburner FeedFlare buttons and more.
Hottaimoijiruna - Adds a self-updating clock to the site for a timezone defined by the blogger.
Inline Ajax Comments - Hides comments until the user clicks on them, and then they fade-in with no reload.
Inline Ajax Page - Allows readers to see a snippet of a post, click a button and the remainder will appear without going to another page.
Tagboard Widget - Adds an auto-updating tagboard to your site that displays new messages as they are posted.
Units Converter - Converts hundreds of different units of Length, Area, Volume, Weight / Mass, Speed without reloading the page.
WP Movie Ratings - Combines data from IMDB with the bloggers movie review and lets the readers add their own rating instantly.
XDTalk - Allows real-time conversation between registered users.