How do I boycott companies that have large investments in Israel?

I've just finished doing a bit of research on Israel, and particularly its treatment of the Palestinians. I am by no means condemning Israeli citizens, but the actions of the IDF and Israeli politicians are frankly disgusting. I refuse to give my money to organisations that support the Israeli apartheid and oppression of Palestinians. Does anyone have a list of companies that have invested large amounts of money in Israel, or who have handled Israeli goods themselves?