As for the subject of mother goddesses, the first one to make such a staggering impression upon me was Tiamat (the Babylonian dragon-mother of creation and chaos). Also included on my goddess list is Brigid, Morrigan, Hecate, Lilith, Hel, Athena, Baba Jaga (the slavic Crone who purifies with her hearth, and flies around in a giant mortar and pestle). Some other goddesses that have surfaced for me are those associated with natural elements, but whom I did not find fitting mythological associations so I only recognize them in their primal wonder: the moon, the twilight, the night.
I share sentiments that they come because they seek out things in people, just as we seek things out in goddesses, and that when that time has passed they move on - and then maybe others come to call on us in their place. This is the case with many of the goddesses I've listed (and gods I haven't). Of those I can say the ones who remain with me are: Tiamat (chaos, creation and primal ways), Brigid (light, poetry, healing, smith-craft), Lilith (passion), Ishtar (love, and the sacred marriage rite between kings and divine consorts such as she), Athena (strength of resolve and cleverness), and Baba Jaga (self-sacrifice); and those just-as-beautiful, non-descript ones. And beginning to feel a pull towards Mary Magdalene.