A polling system is very essential to a blog. My observations are that visitors interact with the website using a voting system more than they do using comment system or sending email. This could be due to the "laziness factor" as interacting with the voting sytem takes just a click or two. Therefore my recommendation is to have a blog poll on your blog for making your visitors interact with your website/blog, keeping their laziness factor in mind.
The poll that I found attractive enough to include in my blogs is from http://www.dpolls.com
Here are others that you can try as well :