Hi,
Here is a new list with all the cloud shapes available for free on the
internet that I could find so far. As you probably know, a vector
cloud is useful if you want to create cartoon illustrations, icons,
website templates and so on. For photo manipulations, where you need
more realistic clouds I recommend you to use cloud brushes or cloud
textures.
http://www.psd-dude.com/tutorials/resources/cloud-shape-vectors-for-photoshop.aspx
enjoy,
John