Headline Split Tester allows you to enter an alternate headline for every post on your blog. (review)
WP Original Source adds a source attribution meta tag, introduced by Google, to single posts and the page header, and adds your permalink to the source attribution meta tag if external urls are not defined.
Posts 2 Posts allows you to create many-to-many relationships between posts of all types.
Regenerate Thumbnails allows you to regenerate the thumbnails for all of your image attachments.
WP Super Cache generates static html files from your dynamic WordPress blog.