Sparrowhawke3D introduced a new plug-in called  Cumulus S3D

Cumulus S3D is a volumetric cloud shape plugin that creates up to 9 puffy animatable clouds in rows.  The clouds grow and fade over time and puffs circulate within the clouds.

With many settings and options the clouds can be arranged in neat rows or be randomly spread.  Towers can rise and fall above the base of the cloud which can be flat, rounded or undulating.

Plug-in can be downloaded at http://sparrowhawke3d.com/CumulusS3D.html