Isaac asks for an example of something that lay people consider to be unethical, that are considered to be ethical by a licensed attorney, because they are permitted by applicable rules. I suggest:

1. Getting a murderer acquitted because the critical evidence was not admitted or some other technicality.
   
2. Finding evidence of a non-client's life-threatening medical condition, but not revealing it to protect a client's financial interest.
   
3. Defending a criminal who commits perjury in the case.
   
4. Getting a 40% contingency fees on a $100k settlement that only required one phone call to make the deal.
   

Igor claims that a lawyer cannot assist a client who is committing perjury, and quotes the DC Bar ethics rules:

Excerpts from Opinion No. 234 of the DC Bar --
Defense Counsel's Duties When Client Insists On Testifying Falsely
Rule 3.3(a) prohibits the use of false testimony at trial. Rule 3.3(b) excepts from this prohibition false testimony offered by a criminal defendant so long as defense counsel seeks first to dissuade the client from testifying falsely and, failing in this, seeks to withdraw when this can be done without harm to the client. ...

In other words, the lawyer can allow his client to commit perjury as long as it wasn't the lawyer's idea. As a practical matter, it is usually not possible to withdraw without harm to the client.

Usually the lawyer just looks the other way. If the client wants to testify with a suspicious alibi, the doesn't ask him if it is really the truth. He merely discusses trial strategy, and the pros and cons of telling such a story.

Isaac says that the lawyers in N. Carolina are required to take:

Remedial Measures
[10] If perjured testimony or false evidence has been offered, the advocate's proper course ordinarily is to remonstrate with the client confidentially. If that fails, the advocate should seek to withdraw if that will remedy the situation. If withdrawal will not remedy the situation or is impossible, the advocate may make disclosure to the court. In the event of such disclosure, it is for the court ...

Ok, so the lawyer has to talk to the client. That is the "proper course". The lawyer "should" withdraw if that will remedy the situation, but that is unlikely. If OJ is going to deny killing Nicole, he is going to do it no matter who his lawyer is. Finally, it says that the lawyer "may" tell the judge. IOW, telling the judge is not required. I still say that this is an example of something that lawyers consider ethical, and non-lawyers do not.

Rahul says:

I was told that when licensed attorneys within the USA use the term 'unethical', they are NOT referring to any moral code, but rather, to the rules of the Bar and/or the court that regulates their professional practice.

That is how I've heard lawyers use the term unethical. It only refers to the rules about what lawyers can and cannot do.