Stratocumulus cumulogenitus

Relatively low clouds in a state carrying much moisture and leading to possible localised showers.

Altocumulus cumulogenitus

Possibly a Altocumulus cumulogenitus cloud, taken at a distance on a summer's day in Bedfordshire, UK.  I believe this is formed from a cumulus congests cloud as the cloud's upward growth is curtailed by the lower temperature in the higher atmosphere hence the "spreading out" effect.

Cumlulonimbus calvus

A section of a cloud carrying plenty of moisture which can grow to a considerable height, representing the next stage of the sizeable cumulus congestus clouds.