Terry Chay

<a href="http://terrychay.com/wordpress-plugins/blog-birthday" rel="nofollow ugc">Plugin Homepage</a>
Inspired by @TwBirthday on Twitter, this shows a simple message in the admin panel on 
their blog birthday.
“Happy 3rd Blogger Birthday! You’ve been around since 11 August 2008.”
“Happy 7th Blog Birthday! The first post on this blog was on 19 November 2004.”
“Happy 1st Blog Birthday! This blog was first registered on 23 July 2010.”
Caveats: 
– Old WordPress admin accounts have a registration date of 0000-00-00 and never have a 
 blogger birthday. 
– Blog registration starts when you turn on WordPress multisite. If you did this, the 
 date may be off. 
– First post assumes that there a post_id=1 and uses the date off that.
<h3>Future Features</h3>
<ul>
<li>Add ability to change the blogger birthday if blank</li>
<li>Add ability to change the blog registration date if first post is different.</li>
<li>4567890012345678900123456789001234567890012345678900123456789001234567890012345678900</li>
</ul>

Blog Birthday

Show a user a notification on their blog birthday.

carman23

You or your members enter a birthdate in WordPress or BuddyPress. This plugin automatically sends an email to such members on their birthday.
You can customize the email that is sent to all Users.
You can request a notification email be sent to you for each birthday email that gets sent, so you know it happened and when.
If you want to contact the author, write to clawrick@gmail.com
Birthday Emails is currently available in English only, though you can customize the birthday email sent, in any language you wish.

Birthday Emails

Automatically send an email to WordPress or BuddyPress users on their birthday.

Blog Birthday vs Birthday Emails