Squirt,
I will try to just explain our beliefs and not harp on about RC errors (though it will be impossible not to mention the odd one in passing) for the sakes of Scott and Victor. I do not want yet another argument with them. I respect them both despite our diferences and hope this can remain amicable. As such I will just briefly answer each of your points below for the moment.
Squirt said:
In this we are almost identical in belief to the RCs. Unfortunately the area in which we disagree was also the major theological cause of the Great Schism. This is the filioque, which is the belief that the Holy Spirit proceeds from both Father and Son. In our view that is a heresy. For the sakes of clarity I should point out that we do have something (and some RCs believe their filioque is the same, whilst others do not) that sounds similar to the filioque. This is that the Holy Spirit proceeds eternally from the Father alone but temporally through the Son. This basically means that whilst He proceeds in His nature from the Father he is sent in time by the Son. If this is what RCs mean then we have no objection to their belief, but their alteration of the Creed and the decree of one of their councils effectively are (for us at least) heretical as both talk of eternal procession from two Hypostases. We can never accept that.
2. Various Marian doctrines.
We have no Marian doctrines. We have certain beliefs which are universally or very commonly held about her, but none have been dogmatised (note that the title Theotokos is a Christological doctrine, not Marian). In most respects our beliefs are the same as the RC doctrines but we do not accept the idea of the Immaculate Conception. There may be other differences, but that is certainly the major one.
3. Baptism -- method of baptism, need for baptism, age of baptism, etc.
Baptism must be (except under exceptional circumstances when economy is applied) performed by triple immersion in the name of the Father, Son and Holy Spirit. Sprinkling is not allowed. It is performed in infancy and immediately followed by Chrismation (annointing - the Orthodox equivalent of confirmation) and first Communion. Baptism is not absolutely necessary in the sense that those who are not baptised may be saved (for instance those martyred for the faith before baptism), but refusal to be baptised would be considered a denial of God.
4. Eucharist/Lord's Supper.
We believe in the Real Presence as a Mystery which we do not seek to explain or analyse. We don't use the term transsubstantiation, but basically agree with the RCC in the essentials. All baptised members of the Church (and only those) may take communion if they are sufficiently prepared (by confession prayer and fasting) to partake worthily, including children. The Eucharist is always administered in both kinds (except by economy, for instance with infants who can't take the Body and get a spoon of the Blood) and leavened bread is always used in accordance with the Greek scriptures which clearly state the bread was leavened and not unleavened.
5. Other sacraments or rituals
I think in this we are very similar to the RCs. We don't formally number the sacraments at 7 and consider there to be several more than this but I see no real difference between us other than in details of practice.
The only real difference between us here is that we have no equivalent to the Vatican or the Papacy. There is no temporal head of the Church and all bishops are considered equal, though some have different jobs. Basically, each local Church is governed by a Patriarch (or equivalent) through the Holy Synod. The Ecumenical Patriarch is first in honour and has the right to chair a Pan-Orthodox Synod, which would include members of each local church's Holy Synod.
Sorry, but this needs a thread in its own right and I can't do it justice here. All I would suggest is that you read St. Athanasios' On the Incarnation, which you can find on the web. That sums up our view pretty well.
Other than that we don't recognise some RC saints and nor do they recognise some of ours, I see little difference here. They have a canonisation process that is markedly different (more forensic as opposed to organic) than ours but that really does seem like a very minor issue.
Hope this helps and feel free to ask further questions.
James