Dirk Weise

This plugin gives you the ability to limit WordPress admin logins based on the country the visitor’s IP address is located in. It uses Maxmind’s GeoIP database which comes in a free lite version.
You can choose between a white- and blacklist mode. In whitelist mode only visitors with IP addresses from the configured countries are allowed. In blacklist mode visitors with IPs from the configured countries are not allowed to login.
<h4>Translation</h4>
So far this plugin is available in English and German. If you are interested to translate the plugin to your language, use the included POT file with a programm like <a href="http://www.poedit.net/index.php" rel="nofollow ugc">PoEdit</a> and get in touch.
<h3>Development</h3>
This plugin is developed by <a href="http://www.dirk-weise.de" rel="nofollow ugc">Dirk Weise</a> as a pet project on <a href="https://github.com/wedi/limit-login-countries" rel="nofollow ugc">GitHub</a>. You are welcome to <a href="https://github.com/wedi/limit-login-countries/issues" rel="nofollow ugc">file an issue</a> or send a pull request.
<h3>Credits</h3>
<ul>
<li>Kudos go out to the guys over at <a href="https://www.maxmind.com/" rel="nofollow ugc">Maxmind</a> for providing a lite version of their GeoIP database for free.</li>
<li>Same to <a href="http://kovshenin.com/" rel="nofollow ugc">Konstantin Kovshenin</a> who has written a <a href="http://kovshenin.com/2012/the-wordpress-settings-api/" rel="nofollow ugc">great tutorial on the WordPress Settings API</a> which helped me a lot while cleaning up the plugin for the public.</li>
<li>Give big hands to <a href="http://sudarmuthu.com" rel="nofollow ugc">sudar</a> for his <a href="https://github.com/sudar/wp-plugin-in-github" rel="nofollow ugc">toolset for deploying WordPress plugins from GitHub</a>. A must have, when developing WordPress plugins on GitHub.</li>
<li>Last but not least I send a thank you note to <a href="http://think0.deviantart.com/" rel="nofollow ugc">Gabriel Oliveira</a> on whose work this plugin’s banner image is based.</li>
</ul>

Limit Login Countries

This plugin gives you the ability to limit WordPress admin logins based on the country the visitor's IP address is located in.

Ivan

The Google Authenticator plugin for WordPress gives you two-factor authentication using the Google Authenticator app for Android/iPhone/Blackberry.
If you are security aware, you may already have the Google Authenticator app installed on your smartphone, using it for two-factor authentication on Gmail/Dropbox/Lastpass/Amazon etc.
The two-factor authentication requirement can be enabled on a per-user basis. You could enable it for your administrator account, but log in as usual with less privileged accounts.
If You need to maintain your blog using an Android/iPhone app, or any other software using the XMLRPC interface, you can enable the App password feature in this plugin, 
but please note that enabling the App password feature will make your blog less secure.
<h3>Credits</h3>
Thanks to:
<a href="https://profiles.wordpress.org/evinak/" rel="nofollow ugc">Oleksiy</a> for a bugfix in multisite.
<a href="https://github.com/pancek" rel="nofollow ugc">Paweł Nowacki</a> for the Polish translation
<a href="https://github.com/FabioZumbi12" rel="nofollow ugc">Fabio Zumbi</a> for the Portuguese translation
<a href="https://www.guidoschalkx.com/" rel="nofollow ugc">Guido Schalkx</a> for the Dutch translation.
<a href="https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=henrik%40schack%2edk&lc=US&item_name=Google%20Authenticator&item_number=Google%20Authenticator&no_shipping=0&no_note=1&tax=0&bn=PP%2dDonationsBF&charset=UTF%2d8" rel="nofollow ugc">Henrik.Schack</a> for writing/maintaining versions 0.20 through 0.48
<a href="http://tobias.baethge.com/" rel="nofollow ugc">Tobias Bäthge</a> for his code rewrite and German translation.
<a href="http://blog.pcode.nl/" rel="nofollow ugc">Pascal de Bruijn</a> for his “relaxed mode” idea.
<a href="http://technobabbl.es/" rel="nofollow ugc">Daniel Werl</a> for his usability tips.
<a href="http://dd32.id.au/" rel="nofollow ugc">Dion Hulse</a> for his bugfixes.
<a href="https://profiles.wordpress.org/users/aldolat/" rel="nofollow ugc">Aldo Latino</a> for his Italian translation.
<a href="http://www.kaijia.me/" rel="nofollow ugc">Kaijia Feng</a> for his Simplified Chinese translation.
<a href="http://www.buayacorp.com/" rel="nofollow ugc">Alex Concha</a> for his security tips.
<a href="http://jetienne.com/" rel="nofollow ugc">Jerome Etienne</a> for his jquery-qrcode plugin.
<a href="http://orizhial.com/" rel="nofollow ugc">Sébastien Prunier</a> for his Spanish and French translation.

Google Authenticator

Personally I feel 2FA should be a part of WordPress core. But since it isn't, plugins like this one are a must-have to secure your sites.

The configuration interface is clearly layed out and the login page fits in perfectly with the default WP login page styling.

This plugin is light-weight, unobtrusive, free and adds that extra layer of security. Should your admin credentials ever be compromised, 2FA will keep your site secure.

Must-have security plugin

Awesome plugin, which is almost always in first group of plugin I've install on new website. Thank you for create and maintain it.

One on few my first-to-install plugin

Google Authenticator for your WordPress blog.

Limit Login Countries vs Google Authenticator