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.

angelorum

Creates a widget to display user’s birthdays of today, and next and past birthdays. Responsive and customizable.
Features: 
– This plugin adds a field in users profile for the user can enter his birthday date, from a calendar jquery popup. 
– Creates a widget to be added to the site. This widget displays to the users who are in birthday today. 
– The widget also allows display the next users who will be in birthday, and the past users too. You can choose the amount of users birthday to be shown. 
– Widget customizable: amount of past and next birthdays to show, show or hide users avatars.. 
– Exports user birthdays to iCal format. 
– Translations: english and spanish.
<h3>Useful links</h3>
<ul>
<li>Oficial website: http://codificando.cl/web/?page_id=92</li>
<li>Developer’s email: jason.matamala@gmail.com</li>
</ul>

Jason Birthday Widget

Good

Creates a widget to displays user's birthdays of today, and next and past birthdays. Exports user birthdays to iCal format. Customizable.

Blog Birthday vs Jason Birthday Widget