Episcopalians - American version of Anglicans. Mostly liberal, welcoming to gay members and clergy. Some acknowledge other religions as valid. Their attitude to evangelism is that actions speak louder than words. Some, such as Grace Church in San Francisco, have said that the mythology of other pre-Christian religions is just as valid as Hebrew mythology.
Methodists - Most UK Methodists that I have met are very liberal and open-minded. Started in the 19th century. Not Calvinist, i.e. they don't believe in predestination.
Baptists - A bit more evangelical, but still unlikely to turn up on your doorstep or leaflet you in the street. Tend to believe that the Bible is the inspired word of God, and that salvation is conferred by acceptance of Jesus as your personal saviour. Started in the 17th century.
United Reformed (Result of a merger between the Congregationalists and Presbyterians in 1972). Some very liberal & LGBT-friendly, but mostly believe that the Bible is the inspired word of God, and that salvation is conferred by acceptance of Jesus as your personal saviour.
Anglicans (Church of England) - Huge spectrum of belief among Anglicans, but mostly a formal liturgy with similar beliefs to other Protestants. Cruising for a huge schism over the issue of LGBT Christians. Have just decided that they should be more evangelical. Oh dear. Founded by Henry VIII when he decided that Anne Boleyn was more likely to produce a male heir than Katharine of Aragon.
Emerging church - May or may not be a good thing - no-one seems able to agree on what emerging church actually means. Some of it looks liberal and some of it looks evangelical. Anyway, it's postmodern.
Unitarians - Not exactly Christian as they mostly believe that Jesus was just a man and that God is One (not three). Don't believe in original sin. Many Unitarians identify as Christian; others are more inclined towards humanism, Eastern religions, and/or Paganism. Many are pantheists, but others are deists. (NB in America, Unitarians merged with Universalists in 1961 to form the UUA.)
Orthodox - Fabulous liturgy and music, apparently unchanged since the fourth century. Lots of lovely incense. Believe that God is both immanent and transcendent. Don't believe in original sin or penal substitution theology. They've known since the 4th century that the creation story was a metaphor. But don't have women priests, and regard homosexuality as a sin. Have married priests but seem rather keen on the perpetual virginity of the Virgin Mary. When they do missionary work, it tends to be a lot more subtle than the other lot, as they don't want to destroy the other culture.
Catholics - The infallibility of the Pope has only been Catholic doctrine since 1875, and the celibate priests thing was only introduced in the 12th century. But they still have a huge hierarchy and loads of money and a history of persecuting heretics, free-thinkers, and scientists. So the Church is pretty bad but some of the actual Catholics are pretty liberal, and invented liberation theology and stuff. Tend to send missionaries overseas to annoy other faiths, rather than actually turning up on your doorstep.
Old Catholics - ceded from the Roman Catholic church in the 1870s in protest at the doctrine of papal infallibility. Tend to be pretty liberal and open-minded, and not exclusivist.
Liberal Catholics - a Christian-flavoured form of Theosophy. They believe that there is a body of doctrine and mystical experience common to all the great religions of the world and which cannot be claimed as the exclusive possession of any.
Moving within the orbit of Christianity and regarding itself as a distinctive Christian church it nevertheless holds that the other great religions of the world are also divinely inspired and that all proceed from a common source. (Wikipedia)
Metropolitan Community Church - church for LGBT people and their allies. Very liberal, but still affirms the Nicene Creed. Generally respectful of other religions.
Quakers (Religious Society of Friends) - there are two wings of Quakerism, liberal and conservative. The liberals are very similar to Unitarians; many of them are humanists, and there are Quaker Pagans. The conservatives are Christians, but still peace-loving honest folk.
Theological and social positions
Distributism - a rather interesting form of anarchism invented by Catholics.
Universalism - in its original sense this meant that everyone was saved regardless of whether they had accepted Christianity. This is also known as apocatastasis. In America, the Universalist denomination merged with Unitarians in 1961 to form Unitarian Universalism. Nowadays, the Universalist element of the name seems to mean the idea that all religions are different perspectives on the same underlying truth.
Exclusivism - the idea that only one religion can be true, and the rest contain only partial truth. Not all Christians believe that Christianity is the only truth.
Penal substitution theology - the idea that God was very angry with humanity, so he sent his only Son to stand in for humanity and be sacrificed to appease his wrath. Not all Christians believe in this; it was formulated in the 11th century by Anselm of Canterbury as the 'satisfaction theory', and then taken up again by the protestants in the 16th century. The alternative is Christus Victor theology - the idea that Christ's death and resurrection represents divine conflict and victory over the hostile powers that hold humanity in subjection.
Fundamentalism - the idea that the Bible is literally true. The term is derived from a late nineteenth-century book called the 12 Fundamentals.
Evangelicalism - the drive to convert people of other faiths and none, in the belief that Christianity is the only truth, or a superior truth. Tend to be charismatic and happy-clappy, but not necessarily.
Original sin - the idea that we all inherit our sinful natures from Adam and Eve, and that we are born sinful.
The Phoenix Affirmations - a call to repentance from ideas of fundamentalism and evangelising, and a series of affirmations about respecting other faiths, the environment, and other people. Very cool.
Queer theology - amazingly cool theology explaining that God really does love LGBT people
Liberation theology - emphasizes the Christian mission to bring justice to the poor and oppressed, particularly through political activism. Its theologians consider sin the root source of poverty, recognizing sin as exploitative capitalism and class war by the rich against the poor.
Process theology - the idea that the Divine changes and evolves. Key thinkers: A N Whitehead, Charles Hartshorne. Has influenced some Pagan thinkers.
Omega Point - idea dreamed up by evolutionary biologist and Catholic theologian Teilhard de Chardin; basically the point at which the Godhead and the world are reunited. Interestingly, chimes in with the reunion of Shakti and Shiva in Hindu theology, and the reunion of Yahweh and the Shekhinah in Jewish theology. The idea of the Omega Point influenced Oberon Zell in his formulation of Gaea Theory (which predated Lovelock's Gaia Hypothesis).
Creation spirituality - a mystical philosophy that celebrates the universe, emphasizes creativity as a key component of the universe, and believes that all people have a divine creative impulse.
Gnosticism - the idea that the physical world is a trap created by the Devil or a demiurge to separate humans from the Divine Reality. This was anathema to orthodox Christians who believe that the world was created by God. Gnosticism is completely the opposite of Pagan views of the world, because Pagans do not believe that we are exiles from some other realm; so whilst we may sympathise with the Gnostics and Cathars for being persecuted, their ideas are utterly alien to a Pagan world-view.
You are all individuals - finally, it's important to remember that Christians have access to teh interwebs too, so they can research other forms of Christian theology and form their own opinions; just because an individual Christian is a member of a particular denomination, doesn't necessarily mean they are signed up to its doctrines. For example, research has shown that even among evangelicals, there is a broad spectrum of views about LGBT people, from complete acceptance to outright hostility.