Which God are we talking about?
According to Wikipedia, the definition of a god is: "supernatural creator and overseer of the universe". Included in this definition are all deities, goddesses and supernatural beings. Arbitrary distinction between old mythological gods and modern gods is unneccessary for this answer. This answer is intended to represent gods and goddesses from multiple cultures giving no creedance to any particular diety.
Since the beginning of recorded history, which is defined by the invention of writing by the Sumerians around 6000 years ago, historians have cataloged over 3700 supernatural beings, of which 2870 can be considered deities. Those numbers are probably a very conservative estimate because we have no accurate information before 4000 B.C. This means any dieties worshipped by man before this period are unaccounted for.
In truth, the possibilities are nearly infinite. For example, in Hindu the entire living universe is merely a unique manifestation of Ishvara. This leads to the fact that there are 330 million "gods or goddesses."
Some examples of the different dieties documented are:
Monotheism:
Judaism: Yahweh
Christianity: God
Islam: Allah
Polytheism:
Greek: Zeus, Hermes, Hades, Hera, Aphrodite, etc...
Roman: Iuppiter, Mors, Terra, etc...
Norse: Odin, Thor, Loki, Njordr, etc...
Hindu: Krishna, Vishnu, Kali, Ishvara, etc...
Chinese Folk (Simple): Shangdi, Mazu, Shou Xing, Tu Di Gong, etc...
Shinto (Japanese): Izanagi-no-Mikoto, Izanami-no-Mikoto, etc...
Celtic: Cernunnos, Damona, Epona, etc...
Egyptian: Ra, Isis, Anubis, Osiris, etc...
Summerian: An, Ki, Enlil, Enki, etc...
Babylonian: Sin, Marduk, Ishtar, Nabu, etc...
Persian: Simurgh, Rostam, Gaokerena, etc...