TwitrCovers has the best collection of Twitter covers available that I’ve seen. All Twitter covers are divided into categories like Nature, Movies, Animals, Art, Games, Quotes, and more.
Simply choose to edit your profile using the iPad app, touch the “Header” button, and choose your preferred cover image. If you’re visiting Twitter using your computer, you can upload your cover by clicking the image of the cog in the upper right-hand corner and choosing to “Edit Profile”. Choose “Design” from the left-hand menu, and then scroll down to the “Customize Your Own” section. Then check out how much better your Twitter cover looks!