SEO Tag Cloud Widget displays the tag cloud in a SEO-friendly way, using a search engine optimized html markup. It looks the same as the default Wordpress Cloud Tag, but with an optimized html markup. You can put it to your sidemenu.
This simple plugin helps you easily tell the search engine bots the preferred version of a page by specifying the canonical properly within your head tag.
Why would you do such a thing? Simply because many black-hat SEO folks abuse duplicate content to gain search ranking and search engine try really hard to detect and penalize them. The last thing you want to do is present yourself as an SEO spammer to search engines.
SEO Friendly Images is a Wordpress optimization plugin which automatically updates all images with proper ALT and TITLE attributes. If your images do not have ALT and TITLE already set, SEO Friendly Images will add them according the options you set. Additionally this makes the post W3C/xHTML valid as well.
The paged comments feature new in WordPress 2.7 is handy for reducing page size, but it introduces the search engine optimization (SEO) problem of putting the same content on different permalinks, as some have pointed out.