As always, I don't want to discourage other quality answers but this thread will be an excellent place to start:

http://www.reddit.com/r/AskHistorians/comments/28n21d/ama_preislamic_arabia/

As the OP advises, check out Robert Hoyland's work on pre-Islamic Arabia. I've just finished it and it's extremely useful. There were more groups besides Arabs as well, and religious beliefs varied between geographical, political, and chronological lines. Christianity, Judaism, and Zoroastrianism were all present. Egyptian religion like the Cult of Isis was also popular. Animal sacrifices were common within polytheist tradition especially regarding camels. Human sacrifice is even recorded to have to taken place.