Mahfuzar Rahman

The MailChimp plugin allows you to quickly and easily add a signup form for your MailChimp list as a widget on your WordPress 2.8 or higher site.
Not sure what <a href="http://www.mailchimp.com/features/full_list/" rel="nofollow ugc">MailChimp</a> is or if it will be helpful? Signup up for a <a href="http://www.mailchimp.com/signup/" rel="nofollow ugc">FREE Trial Account</a> and see for yourself!
After Installation, the setup page will guide you through entering API information, selecting your List and then add the Widget to your site. The time from starting installation to have the form on your site should be less than 5 minutes – absolutely everything can be done via the WordPress Setting GUI – no file editing at all!
<h3>Developer Mode</h3>
You can enable “Devleoper Mode” by adding the following line to your <code>wp-config.php</code> file just above the “That’s all, stope editing!” line.
<pre><code>define('MAILCHIMP_DEV_MODE', true);
</code></pre>
This will enable the MailChimp List Subscribe plugin to operate without the need to connect an external MailChimp Account, and will provide a 
subscription form widget that will not actually submit anywhere.
This will allow you to style and configure the widget in non-production environments that are not publicly accessible.
For more Developer Mode customization options see the following article:
http://connect.mailchimp.com/how-to/how-to-article-configuring-developer-mode-for-the-list-subscribe-wordpress-plugin

Easy Mailchimp Optin Form

The MailChimp plugin allows you to quickly and easily add a signup form for your MailChimp list as a widget on your WordPress 2.8 or higher site.

GetResponse

<h4>GetResponse for WordPress</h4>
GetResponse for WordPress lets you add site visitors to your contact list, update contact information, and add your GetResponse landing pages to your WordPress site as a page. Use it to track site visits and pass ecommerce data to GetResponse. The plugin helps grow your contact list and ensures you have the contact information and ecommerce data to plan successful marketing campaigns.
The plugin features include:
<h3>List-building options</h3>
Encourage people to sign up using all the list-building options and built-in integrations with Contact Form 7, BuddyPress and Ninja Forms:
<ul>
<li>add GetResponse forms anywhere on your site and to your blog posts,</li>
<li>add an opt-in box to comments and registration forms to add site visitors to your list,</li>
<li>add an opt-in box to Contact Form 7, Ninja Forms and BuddyPress forms.</li>
</ul>
Add GetResponse landing pages on your WordPress site to:
<ul>
<li>easily feature new webinar, signup, promotion, download, or sales-focused pages,</li>
<li>use popup, exit popup, and fixed bar forms on the pages to get more signups,</li>
<li>run A/B tests to ensure your page design is optimized for conversions,</li>
<li>easily publish landing pages under your WordPress domain as a subpage,</li>
<li>add contacts without any 3rd party integrations directly after they sign up from one of your landing pages.</li>
</ul>
<h3>WooCommerce – add contacts and collect ecommerce data</h3>
The built-in integration with WooCommerce lets you add customers to your contact list and send ecommerce data to GetResponse. Here’s what you can do with it:
<ul>
<li>grow your list by adding customers at checkout,</li>
<li>export customer list to GetResponse (this option allows you to export custom fields and purchase history),</li>
<li>collect information about customer spending habits, products, purchases made, and shopping carts.</li>
</ul>
<h3>Web Event tracking</h3>
GetResponse for WordPress lets you track visits to your site. Create workflows based on URLs visited. Use advanced search options to identify people who recently visited your site. You can create custom filters and plan your mailings.
Have questions? Head to our <a href="https://www.getresponse.com/help/integrations-and-api#subcat-wordpress-integration" rel="nofollow ugc">Help Center</a> for more information about installing the features in the plugin.

GetResponse for WordPress

Take advantage of your visitors' commentators' and customers' interest. Invite them to subscribe and nurture their engagement.

Easy Mailchimp Optin Form vs GetResponse for WordPress