Clay in that acapella movie.

Boston Bruins Hall of Famer Cam Neely played Sea Bass in Dumb & Dumber. Lawrence Taylor was briefly in The Water Boy. Lance Armstrong was in You, Me & Dupree. Joe Klecko was in Smokey & The Bandit 2. Kareem Abdul-Jabbar was a pilot in the comedy Airplane plus Bruce Lee's Game of Death. Rams Fred Dryer was on a private eye show called Hunter.Alex Karras was the dad on Webster.

Babe Ruth and the other Yankees helped add a feel of authenticty to Pride of the Yankees.
I thought Rocky had a smart touch with Joe Frazer's cameo of greeting the boxers just before the fight.
They couldn't act, but Mickey Mantle, Roger Maris, and Yogi Berra had a humorous cameo in That Touch of Mink with Doris Day and Cary Grant.
This isn't technically a cameo (he wasn't playing himself), but Max Baer, a heavyweight champ that killed a man in the ring, plays a heavyweight champ that wants "credit" for killing another boxer in The Harder They Fall. Baer made several movies and was a pretty good actor.
Babe Zaharias, Alice Marble, and other real-life athletes were in Pat & Mike. They didn't act much, but it was entertaining to see Katharine Hepburn competing aganst them.
This wasn't a cameo, but it was great casting: knuckleballer Tom Candiotti as knuckleballer Hoyt Wilhelm in 61*.
Jockey Gary Stevens did a great job of portraying jockey George Woolf in Seabiscuit.

The Incredible Hulk(2008)- Lou Ferigno
www.Pickthevictory.com

The Incredible Hulk(2008)- Lou Ferigno
www.Pickthevictory.com

He's a HOF tight end, so I think he counts as an athlete.

This may not count because technically he's not an athlete, but Mike Ditka pretty much stole KICKING AND SCREAMING from Will Ferrell.

Mike Tyson in The Hangover
"Does it look like I give a damn?" - James Bond

Patrick "Chewing" in Exorcist 3
" I'm Hardcore To The Bone, I'm Thuggish Ruggish "

chuck norris in dodgeball
dan marino in ace ventura
R
etards
O
rchestrating
C
rappy
K
eynotes

Bob Golic in Saved by the Bell

Dudeshow can you guys forget Cam Neely in Dumb and Dumber?
"Kick his ass, Sea Bass!!!"
"How'd ya know my name was Mac?" - Mac

Babe Ruth in Speedy (1928)
Jackie Robinson in Sesame Street (1970)
Jack Dempsey in Big City (1937)
Roman Gabriel in Wonder Woman (1978)
Red Grange in Zelig (1983)
"You can't send a kid like this up in a crate like that on a night like tonight!"

Don Drysdale, confronted by Louie Nye, in THE LAST TIME I SAW ARCHIE.

I personally crack up every time at the cameos of Nancy Kerrigan and Sasha Cohen in Blades of Glory.
My all-time favorite would be Dan Marino's supporting role as himself in Ace Ventura: Pet Detective.
Nothing really spectacular but Luc Robitaille was a cameo in D2: The Mighty Ducks, along with Chelios, Neely and Gretzky. I think wasn't Jordan also in that, and Kareem Abdul Jabar as well, and I know that Greg Louganis and Kristi Yamaguchi were in that as well.
Other than that, everything else I like has basically already been mentioned.
"This is the uniform of a great man!"
"Does he know you're wearing it?"
Yakko Warner

Ah yes, Keith Hernandez on "Seinfeld" was awesome.
Why would the government lie to us?

Jake LaMotta as the bartender in
The Hustler
(with the late Paul Newman).

Ray Nitschke had a good cameo in the original "The Longest Yard" starring Burt Reynolds. Ray did his best acting when Burt threw a football at his nuts.

I wouldn't consider Kareen Abdul-Jabar's role in AIRPLANE a cameo, that was a supporting role.

Airplane!- Kareem Abdul-Jabaar
hope I spelled that right : )
ColossOkami91's dad says his favorite movie is either The Grinch (2000) or Shawshank Redemption.

From Bang the Drum Slowly: The late Bobby Murcer, my baseball idol as a kid, sliding into second and home plate in the footage used in the "montage" sequence at the old Yankee Stadium. An oddity: The fictional team depicted is obviously the Yankees, but they play at Shea Stadium! In addition, Michael Moriarty's character was intended to reflect a Tom Seaver-like pitcher. This movie had a definite split personality. Finally, this film was made before the Yankees moved to Shea Stadium for two years in the mid seventiesduring the time the old Yankee Stadium was being gutted and renovated.

Hated Favre there.
I actually liked him at the time, but he was horrible.
How can you screw up 3 lines?

Jane's House (1994 TV) - Barry Bonds

Brett Favre in 'Something About Mary.'
"What the hell's Brett Favre doing here?"
"I'm in town to play the Dolphins you dumbass."