Widget Context Plugin allows you to place different sidebar widgets on different pages and posts on your Wordpress blog. Good for having different sidebars for home pages versus individual posts or pages.
Social Profiles is a Wordpress plugin which lets you add links to your commenters' social profiles. The links can be text links or graphical ones, but only registered users of your Wordpress site can input these, thus allowing these profiles to show in their comments on your blog posts.12 different social networks are included - Twitter, Digg, Delicious, StumbleUpon, being some.