Mainly, Lilit(h). Not mythological for me, although both Sumerian and Jewish Kabbalah are generally said as "mythological" by historical references.
I believe in a Goddess that extends beyond a single archetype, while I try to blend archetypes and concepts from various religions and "myths" in order to materialize my own understanding of existence and cosmos.
For me, She is Lilith/Lilit (the fearsome Sumerian Goddess of Winds as well as the Demoness and First Woman not banished from Eden as She fled on Her Will), She is Kali (the fearsome Hindu Goddess and Demoness of destruction and transformation), She is the Yin (the receptive Darkness complementing whilst opposing the Yang light) and the Tao (the wholeness and oneness), She is Al-Lat / Allatu (the Pre-Islam Arabic Goddess of War and Fertility), She is Isis and Bastet and Naunet (Egyptian Goddesses) She is Asherah (Hebrew Goddess consort/sister of Yahweh), She is Ereshkigal and Inanna (Sumerian Goddesses), She is Nuit and She is the Scarlet Woman (Thelemite Goddesses), She is Hekate (the Greek Goddess of Magic and Moon) and Aphrodite (the Greek Goddess of Love) and Athena (the Greek Goddess of Wisdom and Warfare) and Gaia (Goddess of Earth), She is Morana (Slavic personification of Death) and a feminine counterpart of Thanatos (Greek personification of Death as well), and so on, but mainly, Lilith Herself, as beautifully multifaceted as She is, both motherly nurturing and darkly reaping, neither good nor evil, just... Her nature.
I believe in a Sacred and Dark Feminine energy that's inside and outside everywhere, reaching scientific and philosophical concepts such as the entropy, the fields (as in electromagnetic field), the primordial soup from the beginning of earthly life, the quantum fluctuations, the apeiron, the Nietzschean Abyss. She's the shining Darkness, infinite nothingness, omnipresent wholeness and the cosmic Oneness.
In summary, the Dark Mother Goddess, often manifesting to me by Her Lilith's archetype.