Below are great looking YouTube Video Thumbnail images you can use for your own video uploads. The dimensions are 1280px by 720px which covers the dimensions for 99% of devices used to access YouTube channels and videos. Simply press on any image thumbnail and then press on download link.
Subscribe to YouTube Channel Icon (Right Click Save As)
To use this, login to your YouTube channel and browse to Creator Studio > Channel > Branding https://www.youtube.com/branding and use this Branding WaterMark to increase your subscriber base
YouTube Channel Art Template Photoshop
If you have access to Adobe Photoshop and want to find the safe area for your YouTube channel art, then, download this: YouTube Channel Art Template Photoshop