viperchill

ViperBar adds an attractive bar to your site header, which you can use to increase blog or newsletter subscribers. It includes built in styling, Aweber & Feedburner integration, conversion rate tracking, split-testing, themes, and much more.
<a href="http://www.viperchill.com/" rel="nofollow ugc">ViperChill</a>, a blog on Viral Marketing, is the creator of this plugin. If you want to take your blog to the next level, you should read this post on <a href="http://www.viperchill.com/wordpress-seo/" rel="nofollow ugc">WordPress SEO</a>.
<h3>Donations</h3>
You may make donations at http://www.viperchill.com

ViperBar

ViperBar adds an attractive bar to your site header, which you can use to increase blog or newsletter subscribers.

shabbirbhimani

Footer Slideup Form is one of the best ways to ask your user to subscribe to your list without any interruption or blocking and this plugin does exactly that. It adds an FeedBurner subscribe sliding form in the footer of your WordPress blog.
I use and recommend <a HREF="http://imtips.co/feedburner-vs-aweber.html" rel="nofollow ugc">AWeber over Feedburner</a> for RSS to email but my blog readers wanted to have Slideup plugin for Feedburner like I have for AWeber.

FeedBurner Footer SlideUp

Footer Slideup Form adds Feedburner Email Subscription form into the footer where user's can subscribe to your RSS feed using email.

ViperBar vs FeedBurner Footer SlideUp