There are venue restrictions where political speech is restricted, such as on military bases; content restrictions (transmitting classified information to the world); you cannot defraud by saying false things in order to get something, you cannot defame a person, you cannot speak obscenely (though it's hard to tell what counts as "obscenity"). You cannot appropriate other people's property in speaking (i.e. copyright law is a restriction on speech).
The type of speech restrictions seem to pertain to speech and violence caused by such speech. A classic limitation is that you cannot speak "fighting words" (Chaplinsky v. New Hampshire 315 U.S. 568), which in 1942 meant calling someone a "damned racketeer" and "damned Fascist", which the court characterized as "inherently likely to provoke a violent reaction". The court subsequently refined its position on "provocative" speech. In Virginia v. Black 538 U.S. 343 a law against cross-burning was found to run afoul of the First Amendment as a restriction on political expression, but it would be fully consistent with The Constitution to outlaw "cross burning carried out with the intent to intimidate". This states may "prohibit only those forms of intimidation that are most likely to inspire fear of bodily harm".
The current position is that you cannot incite to the imminent use of force. In Brandenburg v. Ohio 395 U.S. 444, the court stated that the First Amendment does not "permit a State to forbid or proscribe advocacy of the use of force or of law violation except where such advocacy is directed to inciting or producing imminent lawless action and is likely to incite or produce such action".
There are myriad laws against threats, for instance in Washington you may not "knowingly threaten(s) to cause bodily injury immediately or in the future to the person threatened or to any other person", and you can't do that ("knowingly cause another to believe that the offender will cause serious physical harm to the person or property of the other person") in Ohio either. You can't get away with threatening "to commit a crime which will result in death or great bodily injury to another person" in California. This class of restrictions on speech seems to be quite robust.
You may not induce panic in Ohio, e.g. shout "fire" in a theater -- I don't know if any other state has such a law.
