The Surface Pro 4 Type Cover by Microsoft and the leather stand cover by Fintie are two good covers for the Microsoft Surface. The Type Cover is available on Microsoft Store, and the leather cover is available on Amazon.com.
Available in six colors, the cover by Microsoft also serves as a keyboard and a trackpad. The cover has magnets along the connection port so that it snaps to the tablet. Despite the name, the Surface Pro 4 Type Cover also works with Surface Pro 3.
Covering the Surface Pro 3, Fintie's leather cover has openings for all ports on the device. The cover also offers a holder for the Surface Pen. It's available in over 20 color and pattern options.