I just found some nice plugins for WordPress on lesterchan.net:

• WP-EMail easily adds an “email this post/page” button.
• WP-Polls: adds an AJAX-style poll support to your blog.
• WP-PostRatings allows users to rate your posts.
• WP-PostViews lets you know how often a post has been viewed.
• WP-Print displays a printable version of your post/page.

There are some other plugins on that site which I haven’t looked at yet.

[Update from 2007-09-11]
Especially for WP-Polls and WP-PostRatings, you should also take a look at the forums. I found some nice help in getting those two plugins to let one vote once every 24 hours (for WP-Polls | for WP-PostRatings). Oh, and if you encountered an error with the gethostbyaddr-function in WP-PostRatings, see this thread in the forum.

[Update from 2007-10-01]
Hm… somehow, WP-EMail does not open a new window any longer, although I changed nothing - the option is still set to popup, but instead of popping up, the same window is used. It might have something to do with my permalinks redirection, I don’t know. I decided to deactivate WP-EMail, since nobody seems to use it, anyway… Sorry, my bad! I have reactivated WP-EMail. Please see this post.