Facebook's news feed is crowded (and more crowded with each passing day). Consequently, visuals play a big role is drawing attention and driving clicks / conversions. This includes feed pictures, profile pictures, thumbnails, etc. With Facebook's new Page Browser, you can quickly get a sense for the imagery that brands and page-owners use.
Some are simple and represent the brand directly (see FootJoy). Some take advantage of the alloted vertical space and are colorful (see HBO's Eastbound and Down)
Obviously the best advice is to test and measure which imagery works best for your brand and your audience.
While their thumbnail is quite different, Facebook's Data page is gorgeous. By cleverly blending the logo into the Facebook page, it looks very natural and clean. While page-owners do not have a ton of room for creativity, this is well done:
