Tanvir Hasan

Quick Top is a customizable plugin that allows you to add a “Back to Top” button to your WordPress site. Customize the button’s appearance and behavior from the settings page.

Quick Top

A customizable button plugin for quickly scrolling to the top of the page.

Vijayakumar Selvaraj

Smooth & simple scroll to top plug & play plugin helps to add “Back to top” in your blog. Activate the plugin & see the result. Nothing to configure. 
Note: This is the initial setup. Adding many features in future releases.
Demo:
1) http://oddanchatram.in/ 
2) http://kkeeranur.com/ 
3) http://vijayakumar.org/

Simple Scroll To Top

This plugin is the most efficient way to add smooth scroll to top option in your wordpress blog.

Quick Top vs Simple Scroll To Top