And although "Gus And Shawn Of The Dead" is not a series finale for 'Psych', it is a season finale and its creator, Steve Franks, was seen visiting the museum. (But the picture I have here is a behind the scenes shot with series star James Roday.) The three of them join a pretty select group, and luckily for them, they're at least still alive to enjoy it. Most of the other members of this group were dead long before TV started adapting their works - Mark Twain, Shakespeare, etc. - and so when they show up in a program, it's as a tele-version.
Another who fits the bill (and still alive) would be Neil Simon, who appeared in an episode of 'The Odd Couple'. Stephen King has shown up in adaptations of his works, but usually as a character not as himself. ('Kingdom Hospital' and 'The Stand' are two examples.)
There's no great significance to this, really. But when has that ever stopped me before?