OO are made up of Coptic, Syrian, Armenian, Indian (two churches), Ethiopian, and Eritrean churches.
EO have 15 Churches, and can be seen in
http://www.oca.org/OCworldindex.asp?SID=2
EO and OO have the same faith, but were split to due differing opinions and misunderstandings at the council of Chalcedon in 451 AD.
EO accept seven councils as ecumenical, while we only accept the first three (the fourth being Chalcedon, which was the cause of a sad schism).
EO's was the Church that split from the RCC, but we were always split anyway, yet amazingly, the Holy Spirit has preserved the essence of faith of both Churches. While many polemic EO's disagree, I can debate that they are wrong, and that they can "second-guess" the fallible Holy Fathers, who regardless of the misunderstandings, continued to preserve the faith, as we know them by their fruits.
Here's an OO article about the two families of the One Holy Catholic and Apostolic Orthodox Church:
http://www.paulosmargregorios.info/English%20Articles/orthodox_churches.html
http://www.paulosmargregorios.info/English%20Articles/3.htm
Now, small other differences can be cultural, ecclesiastical, and traditional (holy father wise). And extra EO councils mean extra canons, which are not part of our Church canons.
Xrictoc anecti!