Sorry if there is an obvious misunderstanding in the title but I was just curious as to the religious make-up of the Middle East before Islam. For example: What would the people of e.g. modern-day Yemen have been in the years before Islam? Jewish? Pagan?
Arab is a potentially misleading term. Before the 20th century, Arab generally meant people from the Arab peninsula. Syrians, Egyptians and North Africans (who now make up the vast majority of people we consider "Arab") were not necessarily considered Arabic unless they were directly, patrilineally descended from Arab conquerors or nomads. The Syrian Aramaic languages and the Egyptian Coptic language both influenced modern Arabic, so it's unclear whether or not we should include them when we talk about Arabic people.
However, no matter how you look at it Arabs, Syrians and North Africans followed a variety of beliefs before Islam including Judaism, Christianity and various forms of "paganism."
In the Arab peninsula there seem to have been a number of tribal religions that were influenced by and jostled with Christianity, Judaism and new Prophetic, Abrahamic religions. The Yemenis were ruled by Jewish kings for a long time on-and-off between roughly 200 bc and 500 ad. Large populations of Jews lived in Yemen, Egypt and other Arab countries until the creation of Israel, when they were largely expelled. There remain significant populations of Arab Jews in Tunisia and Morocco.
As far as Syria, Egypt and North Africa, all these places were ruled by the Romans/Byzantines pre-Islam, so while there were definitely Jewish and "pagan" populations in all these areas, the vast majority of people living in what we now think of as the Arab world were various kinds of Christian, and remained Christian until centuries after the Prophet Mohamed's death.
I believe your question has already been answered in last week's AMA. Here's some relevant conversations from it:
http://www.reddit.com/r/AskHistorians/comments/28n21d/ama_preislamic_arabia/cici0qv
http://www.reddit.com/r/AskHistorians/comments/28n21d/ama_preislamic_arabia/cich7eg
http://www.reddit.com/r/AskHistorians/comments/28n21d/ama_preislamic_arabia/cicq0kg
http://www.reddit.com/r/AskHistorians/comments/28n21d/ama_preislamic_arabia/cicm56n
http://www.reddit.com/r/AskHistorians/comments/28n21d/ama_preislamic_arabia/cicpr8a