1. When you say "no punishment" you meant not justiciable by humans. We have no doubt all transgressions are liable by Heavenly court.

2. There are different sorts of negative Mitzvot that bear no such punishment (here's the list of [all Negative Mitzvos][1]):

 - Negative Mitzvos that are Lav haNitak Le'Ese (Makos 15a) - a negative Mitzvah that has a related positive one to fix it. As a person can fix his misdeed by performing a linked positive Mitzvah there's no immediate punishment. For example, all money related misdeeds bear no punishment because the transgressor can pay back See additional examples [here][2].

 - Negative Thoughts that count as transgressions are also not punishable (probably because we can't have two witnesses), for example, imaging existing of other deities. Or Mitvos of "following one's eyes and heart".

 - Negative Feelings (equals thought?) like not to love transgressors or #50 on the list or #58 - "Not to be afraid of enemies".

 - Negative offensive sayings are also not punishable AFAIK (like offending a widow or an orphan) .

 - Overriding a negative Mitzvah by Shev veAl Ta'ase (not taking actions): for example, failing to help one's fellow (Mitzvah לא תעמוד על דם רעך) by NOT acting is not punishable.

 - Various long lasting Mitzvos, like #46 - Not to dwell in Egypt.

 - Some Negative Mitzvos are too vague to judge, there's no specific defined action, for example, #64 Not to try G-d in His ways - there's no particular action linked to that Mitzvah.

 - IIRC, prohibitions of "Not to become impure by ..." (לא לטמא) are also not punishable retroactively.


  [1]: https://he.wikipedia.org/wiki/%D7%9E%D7%A0%D7%99%D7%99%D7%9F_%D7%94%D7%9E%D7%A6%D7%95%D7%95%D7%AA_%D7%A2%D7%9C_%D7%A4%D7%99_%D7%94%D7%A8%D7%9E%D7%91%22%D7%9D#%D7%9E%D7%A6%D7%95%D7%95%D7%AA_%D7%9C%D7%90_%D7%AA%D7%A2%D7%A9%D7%94
  [2]: https://he.wikipedia.org/wiki/%D7%9C%D7%90%D7%95_%D7%94%D7%A0%D7%99%D7%AA%D7%A7_%D7%9C%D7%A2%D7%A9%D7%94#%D7%93%D7%95%D7%92%D7%9E%D7%90%D7%95%D7%AA