A couple from the Buffalo Bills:
Jim “Machine Gun” Kelly
Mark “Kazoo” Kelso
Doug “The Magic” Flutie
Anthony “A-Train” Thomas
From other teams:
Pete “Go-Go” Gogolak
Junious “Buck” Buchanan
George “Iceman” Gervin
Dave “The Ghost” Casper
Ted “The Stork” Hendricks
Supposedly Mohammad Ali was quoted as saying that he wished he’d thought of that one.
Back to nicknames:
Vinnie “The Microwave” Johnson
Jerome “The Bus” Bettis
Downtown Freddie Brown
Automatic Otto Graham
Fred “The Hammer” Williamson
My family used to refer to Browns QB Brian Sipe as “Noodle Arm” but it never caught on beyond our house. 
How could we (myself included) have gotten this far in the thread without mentioning Julius “Dr. J” Erving?
Magic Johnson. How could I overlook Magic Johnson?
Which reminds me: John “The Count” Montefusco.
Definitely the coolest so far.
Or, more simply, “Hondo”.
Don Mattingly: “Donnie Baseball”
Billy Paultz (NY Nets): “The Whopper”
“Super John” Williamson (also Nets)
Phil “Scooter” Rizzuto
Lance Johnson (Chisox): “1-Dog”
Oh, and how can any list be complete without:
Ozzie Smith: “The Wizard”
Quarterback Chris Chandler was “Crystal Chandelier” because he was injury-prone.
Defensive back Elvis “Toast” Patterson kept getting burned.
Soccer player Jurgen Klinsmann was called “The Submarine Commander” because of his alleged tendency to DIVE! DIVE! DIVE!
Actually, all those nicknames, along with “The Battleship Lorenzen” and “The Round Mound of Touchdown” are from his days here in Lexington at UK.
Coolest current nickname: Cardinal fans, in homage to Stan “The Man” Musial, have dubbed Albert Pujols “El Hombre.”
I can’t believe no one has posted the best one.
Randy “The Big Unit” Johnson
My three favorites:
I’ve always been partial to simple ones like:
“Air” Jordan
“super” Mario (Lemieux - he had more, I know.)
“The Wizard” Ozzie Smith
The best of all time, just for simple matter of factness has to be, “The Great one” Wayne Gretzky.
For pure simplicity you have to love Ernie “Mr. Cub” Banks.
Clyde “The Glide” Drexler was pretty memorable.
Say what you will about Berman-isms but he had a few that were downright fantastic.
Bert “Be Home” Blyleven
Todd " Which Hand Does He" Frohwirth
Jake “Daylight Come And Me Wanna” Delhomme
Andre “Bad Moon” Rison
“Well Dressed” Amani Toomer
As was his college team: “Phi Slama Jama.”
Other nominees:
Saints running back tandem Chuck Muncie and Tony Galbreth were known as “Thunder and Lightning”.
Ted Williams–“The Splendid Splinter”
Saints O-lineman Stan Brock–“The Sheriff”
Roger “The Dodger” Staubach
Saints linebacking foursome–Ricky Jackson, Vaughn Johnson, Sam Mills, and Pat Swilling–“The Dome Patrol”.
Saints RB Craig “Ironhead” Heywood
I always liked Drew Bled-so-much-he-needed-a-tranfusion. Even though it was only used once, in a commercial.
Not a nickname but---- IIRC, (or partially correctly) there was a college basketball player-- maybe in the 80’s–who my friend and I called “Ancient Love-a-Drama”. His name was very close to that, but that’s not quite right. I thought it was one of the best sports names ever but I can’t remember it exactly. Anyone know who I’m talking about?
Ok, yeah, I fully admit this post is weak… I’m just trying to remember this dude’s name!
Most Brazilian soccer stars are known by their nicknames rather than their real names (Pele is actually Edson Arantes do Nascimento) and my favourite is this guy: Kaka.
It is fortunate that he should be so good at what he does, otherwise he would have to find a different nickname.
I’ve always enjoyed the nicknames of the Australian cricketing Waugh Brothers - Steve, the eldest was first on the international scene and was known as “Tugga”, while Mark was overlooked for some time, and became known as “Afghan” - the forgotten war (Waugh) 
Other cricketing nicknames - Mfuneko Ngam (a promising black South African fast bowler who never delivered internationally) was known as “Chewy” (Chewey’N gam), while England left-arm spin bowler Ashley Giles was known as “The King of Spain” after a commemorative mug was produced with a typo.
Favorite rugby nickname - John Eales was called “Nobody” (Nobody’s perfect)
Grim