Favorite cameos from famous people as "themselves"

What are your favorite examples from movies/tv where a famous person shows up as themself?

I think there are two broad categories of such cameos:
(1) The famous person is playing it straight, more or less literally who they are, with the entertainment value coming from the reaction of the other characters, or the incongruity of their presence

(2) The famous person is playing a heightened, fictionalized or exaggerated version of themself, sometimes making fun of one of their known characteristics, sometimes just having weird quirks added.
For the first kind, I can’t think of anything I’ve enjoyed more than Leslie Knope meeting her hero on Parks and Rec.
For the second kind, my favorite two are probably:
(1) Patrick Stewart pitching a script in which he would use mental powers to be a perv on Extras
(2) Bojack Horseman’s recurring appearances from gun-toting lawbreaking “Character Actress Margo Martindale”

Mark Hamill on “Just Shoot Me”. Not really a cameo, but he followed Star Wars fan Finch around until Finch became tired of him, just to show him how annoying it was.

Mel Torme on “Night Court”. Judge Stone has to send his idol to jail.

Brett Favre in There’s Something About Mary.

“Brett Favre? What the hell are you doing in Miami?”

“We’re in town to play the Dolphins, you idiot.”

I like Bill Murray in Space Jam

I prefer him in Zombieland.

Clayton Moore and Jay Silverheels in the classic Jeno’s Pizza Rolls commercial.

Ian McKellen explaining acting in Extras

More examples of this include Neil Patrick Harris in Harold & Kumar Go To White Castle and Tim Stack in My Name Is Earl.

Bill Buckner’s appearance (and redemption) on Curb Your Enthusiasm was both funny and heartwarming.

James Earl Jones driving Sheldon crazy with his wild night out on the Big Bang Theory was a riot.

Chuck Mangione in King of the Hill.

Started off as a minor joke about has-been celebrity spokesmen, but after repeated appearances became a running joke of how much of a has-been he was. Only time I can recall where a celebrity cameo basically became a fully fleshed out character with a complete arc.

I liked when Madeleine Albright, Hillary Clinton and Colin Powell showed up to give Secretary McCord advice on an episode of Madam Secretary.

Blake: I asked them to wait in your office. It was their office, too, after all…

Not really a cameo, since the episode was built around it, but since larger appearances have already been introduced…

Robin Williams as himself on Mork & Mindy. Him and Mork looking alike was a running gag - everybody except Mork saw it…he was insulted by the comparison, considering Robin pretty ugly, as well as finding his name obscene - and he showed up near the end of the episode, where he was on for a bit, then had a serious conversation about the nature of celebrity with Mork & Mindy. (Mork’s report to Orson was a bit depressing, on that one.)

Condoleeza Rice on 30 Rock. Conan on 30 Rock.

Bob Barker in Happy Gilmore

There’s always Dick Van Dyke’s appearance on Mary Tyler Moore’s Mary. Mary played the lead of a variety show, and they realized she looked a lot like the actress who played Laura Petrie, so they wrote a couple of sketch about it. The real Van Dyke was stuck and traffic and didn’t show up until the end of the show (Rob Petrie was in the sketches, played by Van Dyke). Finally, he showed up, with the great exchange.

Mary: You know, I was up for a role in the Dick Van Dyke Show
Dick: Oh? What happened?
Mary: Well, it was close, but at the last minute Rose Marie got the part.

Randy Travis and Wynonna Judd on KING OF THE HILL.

Kurt Vonnegut in, “Back to School.”
Least favorite: el Prez in, “Home Alone 2.”

Carl Weathers as a cheapskate on Arrested Development.

Bruce Campbell as a sleazy version in my name is Bruce.

Tom Petty as nameless but it’s totally Tom Petty in the Postman.

Jean-Claude van Damme as semi-unflattering in JCVD.

Malkovitch. Malkovitch! Malkovitch, Malkovitch…

Mel Torme on Seinfeld, singing to a mentally challenged (he thinks) Kramer at a charity banquet.

This morning, I saw the episode of MTM where Ted finally wins a TEDDY Award and fawns over Walter Cronkite when he shows up to pay a visit to Lou Grant.

Elvis Costello, Sean Penn, and Harry Dean Stanton as Charlie Harper’s “support group” on Two and a Half Men.

President Richard Nixon on Rowan and Martin’s Laugh-In. Sock it to MEEE.

No one really thought of him as a good-natured guy at the time.

Marshall McLuhan in Annie Hall