Attached Link: http://www.google.com/search?hl=en&q=photoshop+filters&spell=1

There are some resources for plugins (see link), and maybe you should look for tutorials which use the 'coulds' filter from PS itself as a start. If you don't want to spend money on it. I usually use Bryce to get my realistic clouds, I think that can do even better that KPT 6, you can see that in the Bruce galleries around here.