Dave Thomas, comedian
Dave Thomas. founder of Wendys
wasn’t there another semi-famous Dave Thomas as well?
Also, Dave Thomas, Patriots tight end.
Michael Jordan, NBA
Michael Jordan, CEO of EDS
Not sure if these count, but:
Kareem Abdul-Jabbar (formerly Ferdinand Lewis “Lew” Alcindor)
and
Karim Abdul-Jabbar (formerly Sharmon Shah, now Abdul-Karim al-Jabbar after being sued by Kareem Abdul-Jabbar/Lew Alcindor).
Robert L. Johnson, founder of BET.
Robert E. Johnson, executive editor of Jet.
And for a while some years ago, there were two Mark Carriers in the NFL.
Also, a Kurt Warner and a Curt Warner at different times.
The Wikipedia disambiguation page has 44 entries for Steven Smith. It does not even contain the fairly famous Steve Smith, a flamboyant American Olympic pole vaulter in the late 70’s, or my buddy from high school, who is not famous at all, but got me to start noticing all the famous Steve Smiths. There was a very famous Steve Smith, American football player, and a pretty famous Steve Smith, NBA all star.
I think you could probably put together a pretty decent basketball team only staffed by Jason or Jayson Williams.
Also, there’s Jack Johnson, musician, who is arguably more famous than the other Jack Johnsons. And also there’s Robert Johnson, the blues guitarist who supposedly sold his soul to the devil to gain his mastery of the instrument.
And Mike Collins, comic book writer/artist. Creator of one character named Thunderbolt, & later writer/artist of another one (a version of Pete Morisi’s).
There’s Michael Jackson the beer writer.
There are also two Vanessa Williams, both of whom happen to be African-American. The more famous one is the singer/actress/former Miss America now starring on Ugly Betty. The other one was on the first season of Melrose Place and has done a few other TV and movie stints.
The Green Lantern spells it “John.”
The psychic’s last name is “Edward.”
But yes, those are amusing.
The late actor Kevin Smith, of Xena fame.
Comic shop owner, comedian, auteur, & occasional actor Kevin Smith.
(Or, the dead one & the fat one.)
Oh, I forgot about that! The famous one got into acting later, so the less famous one has the name under SAG. IIRC, they were once in two different TV shows on at the same time, using the same name.
The famous one is now “Vanessa L. Williams.”
Thanks, I needed that! 
Jesse James, bank robber.
Jesse James, car and bike guy.
Jessie James, “newly minted pop diva.”
Barefoot Babe [noparse]Jesse James[/noparse]
Joe Jackson, Michael’s father.
Joe Jackson, British musician.
“Shoeless” Joe Jackson, baseball star.
Not identical, but easily confused:
Tanya Harding, female athlete whose career was embroiled in scandal.
Tonya Harding, figure skater.
Dammit! You beat me to it! 
Dr. Dre - Rapper
Doctor Dré - Host of “Yo! MTV Raps”
“I’m OK, You Could Use a Little More Salt.”
Clement Wood, author of a famous rhyming dictionary.
Clement Wood, author of the famous 26 letter understandable pangram MR JOCK, TV QUIZ PHD, BAGS FEW LYNX.
Alan Campbell, Dorothy Parker’s 2nd & 3rd husband.
Alan Campbell, who played Joe Gillis in the Broadway version of Sunset Boulevard.
Dan White - Harvey Milk’s assassin
Dan White - character actor in mostly Westerns in the 30s - 70’s
Dan White - Arizona Wildcats QB in the 90’s
Danny White - Dallas QB in the 80’s
Danny White - keyboardist of Matt Bianco
Daniel White - lawyer, writer, editor, humorist
[Steve Howe](http://en.wikipedia.org/wiki/Steve_Howe_(basebal), famous substance-abusing baseball player and Steve Howe, guitarist for Yes and Asia.
Another rock n’ roll and baseball combination: Dodger pitcher Bob Welch, who struck Reggie Jackson out in the 1978 World Series and Bob Welch, former member of Fleetwood Mac, who did not strike Reggie Jackson out in the 1978 World Series.
If we’re going to allow John Stewart, the Green Lantern, let’s match him up with the late musician John Stewart of the Kingston Trio, who wrote the Monkees’ "Daydream Believer and recorded the hit single “Gold” in 1979 as a solo artist.