That depends on what you want to show, of course. What kind of example do you have in mind? What kind of information are you showing?

Here are some examples of non-button rectangles:

http://www.windowsphone.com/en-us/store/app/weather-clock/ec...

http://www.windowsphone.com/en-us/store/app/weather/171f3a75...

The differetiators here seems to be that 1) the rectangle is not a square 2) the rectangle has rounded corners

edit: and I guess 3) the rectangle is not "flat", it has a gradient, 4) it's not colored, it's transparent grey, unlike any clickable rectangle in the system. .... (basically, it's fairly easy to differentiate between a clickable square tile and a pure informational rectangle)

Those UIs look quite cluttered and unclear to me, but I suppose a weather app isn't the best benchmark.