What are the limits on the right to free speech?

EXTREMLY basic rundown on the traditional classic unprotected categories of speech:

Incitement (Brandenberg): speech directed or intended to producing imminent lawless action, and is likely to product such action.

False statements of fact (New York Times v. Sullivan): for matters of public concern that defame public officials, the statements are unprotected if they are known to be false or are recklessly made with regard to their falsity, called "actual malice." For matters of public concern that defame private citizens, the statements are unprotected if made negligently under a case called Gertz. On matters of private concern, they may be unprotected regardless, through a consideration of the whole record.

True threats (Virginia v. Black): those statements where the speaker means to communicate a serious expression of an intent to commit an act of unlawful violence to a particular individual or group of individuals.

Obscenity (Miller v. California): the average person, applying community standards, considering the work as a whole, finds that the speech appeals to the prurient interest; it is patently offensive depiction, applying community standards, of sexual conduct, as defined by statute; and as a whole, it lacks serious literary, artistic, political, or scientific value.

Child pornography (Ferber): the speech visually depicts minors engaged in sexual acts or lewdly exhibiting their genitals.

Fighting words (Chaplinsky): speech that tends to incite an immediate breach of the peace, or words that by their very utterance inflict injury, or an emotional distress tort.

You can't go around threatenning to kill the Prisident of the U.S,are threatenning to do ant kind of terrorist attack against the U.S.