My two penn'orth:
> Paganism is any religion which has developed naturally from religious experiences within a community, rather than being founded by someone claiming to be a prophet. It can have a continuous history, like Shinto in Japan or African Traditional Religion, or it can be reconstructed after having been suppressed by Christian or Muslim persecution, like the Heathen or Canaanite religions.
> Goddess spirituality is as described by Quintessence. I'd add that it can exist within a broader pagan tradition, like the cult of Isis (Hellenic or Egyptian) or Shaktidharma in Hinduism.
> Neopaganism is any religion founded in modern times which attempts to have the features of Paganism without being a continuation of an older tradition. Wicca, pagan Druidry, some forms of Satanism, eclecticism. Gerald Gardner, the founder of Wicca, thought he was a reconstructionist, but he was mistaken.
> New Age is a system of personal development rather than a religion.