pjf: none of the tickets issued by
IATA member airlines are transferrable. All tickets are, per IATA regulations, personal. If a ticket is refundable or endorsable, however, you can use the value of the ticket to pay for a new one. This is called reissuing a ticket. Airlines usually charge a fee in the $50-100 range for reissues. Scalping does not exist on this market because as you reissue, you tap into the same seat inventory and fare rules as everyone else. This means that holding a ticket does not give you any advantage over just paying for the new one in cash.
Pre-9/11, you weren't legally required to produce identification on domestic flights within the United States. This enabled a big secondary market for non-changeable, non-refundable tickets to exist. Since then, government regulations have plugged this loophole. Civil liberties activists are challenging the constitutionality of the current ID requirements, however.