ThemesWP

Using Ultimate Custom ScrollBar for customize scrollbars, you get a very elegant and unique site. Consistent scroll behavior for every device. You can change scrollbar size, colors, animation, position from this settings page.
Plugin Features
<ul>
<li>Simple installation & activation</li>
<li>Supported touch devices.</li>
<li>Unlimited colors.</li>
<li>Lightweight.</li>
<li>Enable/Disable Option.</li>
<li>Easy Option Panel.</li>
<li>All browser supported</li>
</ul>
Free Options
<ul>
<li>Enable/Disable ScrollBar : You can enable or disable scrollbar using this option.</li>
<li>Cursor Width : You can increase or decrease cursor width using this option.</li>
<li>Rail Background Color : You can change rail background color from this color picker.</li>
<li>Cursor Color : You can change cursor color from this color picker.</li>
<li>Auto Hide Mode : You can select scrollbar auto hide mode from this selectbox.</li>
<li>Included all free options.</li>
<li>Cursor Border : You can control cursor border using this option.</li>
<li>Cursor Border Radius : You can control cursor border radius using this option.</li>
<li>Scroll Speed : You can control scroll speed using this option.</li>
<li>Mouse Scroll Step : You can control mouse scroll step using this option.</li>
<li>Emulate Touch : Enable cursor-drag scrolling like touch devices in desktop computer.</li>
<li>Minimum Cursor Height : You can set the minimum cursor height.</li>
<li>Bounce Scroll : Enable scroll bouncing at the end of content as mobile-like.</li>
<li>Horizrail Enabled : You can control horizontal scroll.</li>
<li>Rail Align : You can control alignment of vertical rail.</li>
<li>Rail Valign : You can control alignment of horizontal rail.</li>
<li>Enable Mousewheel : You can control Mousewheel using this option.</li>
<li>Enable Keyboard : You can enable or disable keyboard events using this option.</li>
<li>Hide Cursor Delay : You can set the delay in microseconds to fading out scrollbars.</li>
<li>Enable Scroll On Selection : You can enable auto-scrolling of content when selection text.</li>
<li>Cursor Drag Speed : You can set speed of selection when dragged with cursor.</li>
</ul>

Ultimate Custom ScrollBar

Using Ultimate Custom ScrollBar for customize scrollbars, you get a very elegant and unique site. Consistent scroll behavior for every device.

SoftHopper

WordPress custom scrollbar is highly customizable WordPress plugin. Features include vertical and/or horizontal scrollbar(s), adjustable scrolling momentum, mouse-wheel, keyboard and touch support, ready-to-use themes and customization via CSS, RTL direction and many more.
You can change almost 100+ demo style, ScrollBar scroll speed, Showing ScrollBar arrow button mode, ScrollBar auto hide mode, ScrollBar auto expand mode, ScrollBar moving mode by keyboard & other settings by using the options and shortcode of this plugin. 
<a href="http://wordpress-custom-scrollbar.softhopper.net/" rel="nofollow ugc">Click here</a> to see a live demo
Features include:
<ul>
<li>100+ scrollbar demo</li>
<li>Full page Scrollbar</li>
<li>Single Content Scrollbar</li>
<li>Custom Selector Scrollbar</li>
<li>Vertical and horizontal scrollbar support</li>
<li>Highly Customizable</li>
<li>Enable TinyMCE Button</li>
<li>ScrollBar scroll speed control</li>
<li>ScrollBar arrow button mode control</li>
<li>ScrollBar auto hide mode</li>
<li>ScrollBar auto expand mode</li>
<li>ScrollBar moving mode by keyboard</li>
<li>Shortcode Powered</li>
<li>Translation Ready</li>
<li>Responsive for all devices</li>
<li>All major browser supported</li>
<li>Easy to handle</li>
</ul>

Custom Content Scrollbar

WordPress custom scrollbar is highly customizable WordPress plugin.

Ultimate Custom ScrollBar vs Custom Content Scrollbar