Neil Simon

Enter an email address and available contact information is displayed:
<ul>
<li>Photo</li>
<li>Name</li>
<li>Demographic information</li>
<li>Personal interests</li>
<li>Clickable social links (LinkedIn, Twitter, Facebook, …)</li>
<li>Recent <a href="http://twitter.com/" rel="nofollow ugc">Twitter</a> updates</li>
<li>Recent <a href="http://plancast.com/" rel="nofollow ugc">Plancast</a> plans</li>
<li>Optionally, emails the displayed contact information to any valid email address</li>
</ul>
Contact information provided by <a href="http://fullcontact.com" rel="nofollow ugc">FullContact</a>.
Email services provided by <a href="http://sendgrid.com/" rel="nofollow ugc">SendGrid</a>.

RainmakerMoxie

RainmakerMoxie (BETA-limited support) is an interactive sidebar widget. Enter an email address and it displays a photo, name, social links and more.

samwilson

A simple address book plugin.
You can view and edit addresses (names, addresses, phone numbers, email addresses, etc.) in the administration interface (under Manage > Addressbook or as its own top-level menu item), or embed a read-only list of addresses in posts and/or pages.
Addressbook features:
<ul>
<li>Gravatar support for both address lists;</li>
<li>hCard microformat support in the address list.</li>
</ul>
Still to come (hassle me if you want these now):
<ul>
<li>Import/export to a bunch of formats;</li>
<li>Firefox Operator addon scripts to export external addressed into Addressbook;</li>
<li>Pass various options to the <code><addressbook /></code> element, to sort and limit and whatnot;</li>
<li>Templates for the address list display;</li>
<li>Photo upload (probably over-ride the Gravatar, and show a note that there is a Gravatar?);</li>
<li>Custom fields;</li>
</ul>

Addressbook

A simple address book plugin.  View addresses in the admin back-end or embedded in a post or page.

RainmakerMoxie vs Addressbook