Fluffy White (or Grey or Bluish) Clouds
This is by far the most common kind of thing that comes up when you do image searches for the word 'heaven'. I honestly, truly, believe that heaven will be much more interesting and enjoyable than an otherwise empty sky, with clouds in it.
This photo album shows many other things, all of which heaven will also be much more enjoyable than. And all of which (at least in my opinion) would be better than the fluffy clouds that heaven is usually depicted as.
See also: What If You Actually Believed You're Going to Heaven?