Marekki’s Watermark Plugin for Wordpress inserts your logo or text in your wp-upload pictures. You can watermark in two different ways.

Insert watermark while a picture will be uploaded, or
Insert watermarks on all chosen pictures from a directory [like wp-uploads] on your web-server.

Get Watermark plugin for Wodpress here.
Updated : June 06 . 2008
Marekki’s Watermark Plugin has [...]

Auto Delete Posts is a plugin to automatically delete posts after a set expiration date. The plugin deletes all posts regardless of category that are older than a set expiration date. [Source]
The expiration is set in number of days.
Download Auto Delete Posts v0.5 wordpress plugin.

Translate Widget for Wordpress
It adds little flags to your sidebar, which will take you to a translation of the current blog page. It uses Google Translate, but removes the frame, so it looks quite nice! Once you’re in one language, you can browse around the blog, and everything stays translated. You can just click on [...]

Get statistics like visitor’s browser type, OS, total hits etc. from the admin panel of your wordpress blog with WP-Shortstat plugin.

Wiki page for WP-ShortStat
Direct Download for WP-ShortStat

Add a contact form on your wordpress blog. The advantage of this particular plugin is that it comes with an anti-spam challenge question. This means no spam mails in your inbox from bots.

Download the WordPress Contact Form with Spam Protection.
Upload it to the plugins directory and activate it. To bring up the contact form, you [...]

YouTube Related is a wordpress plugin that shows related videos from youtube, based on the tags you’ve provided in Simple Tags Plugin.

What does the plugin do?

It Integrates with “Simple Tags Plugin” for WordPress (modify code to get tags from other plugins or places)
Then, it takes the first Simple tag found and uses it [...]