My first time seeing these clouds. Thought they were really unique, so I had to grab the camera and try to save them. Thanks for the comment.
The first time I saw them (over my house) they scared me, but I learned they are not a harbinger of bad weather. The whole sky was full of them and it looked spooky. I think this is a recently named cloud type, called mammatus clouds. There is a Wikipedia entry about them that has some info and links to images.