Robert Michel, the minority leader of the House of Representatives in the 80’s and early 90’s.
John Shalikashvili, Chairman of the Joint Chiefs of Staff under Clinton.
Shaun Livingston and A.J. Guyton, NBA basketball players.
I was in two school systems as a kid. For the one I was in for most of my childhood, the two truly notable alumni are Tim Conway and Calvin and Hobbes creator Bill Watterson. The high school that I ended up at has graduated a couple of NFL players, neither of whom are household names.
I attended two high schools, Wikipedia states the following alumni:
North High School, Phoenix, AZ
Michael Carbajal, Former Light Flyweight Champion
Wayne Newton, Entertainer
Barry Goldwater, US Senator (republican) (AZ)
…and both of my parents. 
Central High School, Phoenix, AZ
Cindy McCain, wife of Senator John McCain
Bryan Colangelo, Toronto Raptors General Manager (Son of Jerry Colangelo, who was good friends with my first boyfriend’s dad)
Richard Page, lead singer for pop rock group Mr. Mister.
Chad Smith from the Red Hot Chili Peppers. That’s the only one I know of.
Nobody. It’s rather unfortunate. I went to a classic suburban high school (opened 1948, closed 1984) and in its history, no one famous pased through there. Even counting semi-famous, about all we had was one guy who went to Hollywood and sold a few shows and one successful businessman (who later got into tax trouble) who owned the St. Louis Blues hockey time for awhile. Granted we graduated our share of doctors, lawyers, educators, etc., but virtually no one who gained any kind of notoriety outside of their own profession.
Even my first wife’s tiny high school can claim a former Playboy centerfold. Sheesh!
Charles Manson, though he didn’t graduate.
Other than that, maybe Jim Dine. Or Jerry Rubin.
Greg Olsen, current Tight End for the Chicago Bears
or
Barbara Dare, 80’s porn star
Depends on the audience, I guess.
“Macho Man” Randy Savage, according to Wikipedia. Snap into a Slim Jim!!! 
Denise Richards went to my high school but only for her freshman year. She was born in '71 so this means my sister probably spent her freshman year with her.
Natalie Merchant.
What he said (Class of 2005)
I attended Cheltenham High School in Montgomery County, PA.
Reggie Jackson.
Richard Levinson and William Link. Met in my H.S., became writing partners. Created “Colombo” as well as numerous other stories, characters, made for t.v. movies, etc.
Benjamin Netanyahu. Also, his brother Yonatan Netanyahu who was killed Uganda during Operation Entebbe.
Michael Brown, 1985 Nobel Prize in Medicine
Tom Feeney, Congress, R-FL
Glenn Fine, Inspector General, US Dept. of Justice
Mark Levin, radio talk show host
Wallace Triplett, NFL Player
Oh- I went there. 
There are others.
Supposedly Jackie Chan for a few weeks but I am yet to find anyone who remembers him being there. At that time I don’t think we had one Asian student at our school. And he can barely speak English now so surely he would have been noticeable then. Most people remember him hanging out at his parent’s restaurant years later.
Vernon Kay for secondary school and The Verve for sixth form.
D. J. Flick, Grey Cup-winning wideout for the Saskatchewan Roughriders, and…well, that’s about it.
OK, one other. My best friend in high school was the 2002 WXW Announcer of the Year and is still a well-known pro wrestling photographer, story-teller, and part-time actor. See you at reunion this year, Eric.
Let’s see, there’s a state assemblyman if local politics is famous and the general manager of a decent minor league soccer team. Neither one is “famous”, they just get interviewed by the local rag every now and again.
Otherwise you’re looking at people who manage to squeak into things that could make them famous like a few small time actors, a few musicians and a few writers. They could be famous eventually, but they’re not yet.
Sarah Silverman.
Although a friend of mine became a film maker and just won the “Best Feature Film” award at the Monaco film festival, so he might give her a run for her money.
My high school? Wikipedia lists four hockey players and an Olympic swimmer.
Although, it looks like the school website was dramatically-modernized since I last checked.
Ellen Barkin, Billy Dee Williams, Eartha Kitt, Wesley Snipes and Al Pacino.
I attended at the same time as Ellen (she apparently was in my class), but don’t recall her. I guess she didn’t stand out. We had a lot of characters.
Either half or all of My Chemical Romance. -_-;;
One of my friend’s sisters is even married to that guitarist with the ridiculous amount of hair.