While Judaism offers a great deal of latitude for the freedom of expression, I do not think it would be correct to characterize freedom of speech as a 'Torah value' or a 'Jewish value,' at least in the sense that we define freedom of speech in the contemporary world.
When we speak of freedom of speech, we think of the American Bill of Rights. In Jewish law and in Scripture, Judaism is defined not so much by individual freedom as it is by communal responsibilities and obligations. American law is structured to protect the individual from governmental controls. The primary purpose of Jewish law is to create a 'nation of priests and a holy people.' It is more concerned with promoting righteous living than it is with celebrating the autonomy or the rights of the individual.
There are limits, then, placed on self-expression particularly when it comes to words that could harm others. This goes far beyond laws against slander in our society. Gossip, even when it is not malicious, is prohibited by Jewish law and is considered a sin from a Jewish standpoint. In addition, limits were often placed on the community when it came to the expression of ideas outside the accepted norms of Judaism. The rabbis could resort to ex-communication to place controls on self-expression within the context of community as we see in the case of Benedict Spinoza.
That being said, there is a great deal of room in Jewish discourse for the expression of dissenting points of view. Talmudic law is not as concerned with presenting the official point of view as it is with arguing the pro and con of each issue. Minority opinions are included in the Mishnah and the Talmud even when they are not the accepted point of view, as we see in the cases of Beit Shammai and Beit Hillel. Even though the School of Hillel is almost always the accepted point of view in matters of Jewish law, the rabbis took the opinions of the School of Shammai seriously. At the end of the day, however, the official point of view must be accepted as the law no matter what the theoretical arguments for the other point of view may be.
One of the best known examples of this conflict between individual expression and communal norms is the story of the aknai oven (Bava Metzia 59a-b). In this famous case Rabbi Eliezer took exception with his colleagues regarding the ritual purity of a certain type of oven. Rabbi Eliezer offers a series of 'proofs' for his point of view which are entirely circumstantial; he says that if he is correct then, a carob tree will uproot itself and move to another spot; the river will flow backwards; that the walls of the academy will fall. In each case the sages reject his 'supernatural' proofs. In the end Rabbi Eliezer says, "If the halachah agrees with me, let it be proved from Heaven!’ Whereupon a Heavenly Voice cried out: ‘Why do you dispute with Rabbi Eliezer, seeing that in all matters the halachah agrees with him!’" Despite the voice of God taking sides the rabbis again reject Rabbi Eliezer's point of view by saying: "The Torah is not in heaven! …the Torah had already been given at Mount Sinai; we pay no attention to a Heavenly Voice, since it is written in the Torah, 'After the majority must one incline.'" Less well known is the end of this story: the rabbis excommunicated Rabbi Eliezer because he was unwilling to accept the majority opinion.
Whatever the classical point of view may be, I would have to say that we value freedom of speech today as if it were a "Torah value." Living in a world in which self expression is deeply important and in which pluralism is part of the vitality of the contemporary Jewish community, we recognize that we gain a great deal by encouraging freedom of expression in the Jewish community. Like the sages of Talmud, we affirm the teaching Lo bashamayim hee, "the Torah is no longer in heaven, and there are many different ways of reading Torah today. As Jews we have often been the victims of political and moral oppression. There is much more to be gained by being advocates of freedom then there is by curtailing the freedom of the individual.