Good thread! I'm glad of this thread as I often wonder these things too. I have a local church in my area that is a "Black Mennonite" ? church and they don't dress plain at all though the women do cover their heads in church. They are part of the Mennonite Church USA. I'm not sure if they are considered to be less "orthodox" or what have you, but my question is (and I honestly do not seek to debate, just question) are there groups that are considered to be unorthodox by others and what is considered to be orthodox Anabaptist? Any books or links would be great! 
Orthodox really isn't a word you will hear Mennonites use a lot. One thing Anabaptists and Quakers have in common is a greater emphasis on right practice in daily life than in right belief. Faith is more a matter of faithfulness than theological opinions.
Some groups of Mennonites are more strict in outward things like plain dress, head-covering, etc. Generally speaking, you will see Mennonites trying to discern God's will from the Bible as a community. The obligation to give and receive counsel within your church is taken very seriously. Within American society, this can be seen as strange to outsiders, as everyone seems to be in everyone else's business, but it differs from authoritarian religions because there is no concentration of power in particular leaders. Everyone is encouraged to give counsel, not just a few, and when there is a controversy, the community will try to work it out together.
Because of this, you will see a fair amount of autonomy in local congregations, although the same obligation to give and receive counsel applies between congregations as within them. A denominational association of Mennonite churches will have a Board of Reference and Counsel, which is a group of people elected from various congregations because they are recognized as wise. As the name implies, a congregation can refer difficult questions to them for counsel, and you may see members of this board visiting a business meeting in a church that is troubled by some kind of controversy, but they are counselors only, not decision-makers. Decision-making is done by the congregation as a whole.
It is basically a self-regulating system. The leader of business meetings is called a moderator. As the name implies, this person's job is not to lead, but just to facilitate orderly discussions. As you might imagine, most Mennonite congregations are not very large, partly because this system can get unwieldy in larger groups. Mennonite business meetings can go very late into the night, as many details are discussed by the entire congregation.
