This isn't really a post of my site, but I just finished what I guess you would call a mod. It allows the administrator to send an email to all users at one time.
To install, unzip the file and edit the "$from" to the email address you want to send your email from. Then upload this to your admin directory. If you want you can add a link that is viewable only to superadmins.
I started on it earlier today, and litterally just finished. It is only the bare essentials for mass mailing. It doesn't automatically add a link in the admin panel or anything like that. Since the mods db is closed I thought I'd post it here.
It looks solid, also does what it said. So looking good.
Although you should check it with Firefox as well. Didn't work there. Second tip is to dowload Digi's newsletter from the infusions on this page, rip out the parts for sendemail. His "bulk" email won't end up in the spam folder :)
I've found a small problem with the script, but it is minor. In some cases you may not be able to select the message field with your cursor. I am looking into the problem, and will keep you updated.