I was born in 1988 so going to stick to people I have a good enough memory of.

Phil Taylor - the man is a machine. must be as dedicated in practice as anyone in any sport and continues to pile up the titles season after season.
Floyd Mayweather - if there is a better pound-for-pound boxer on this planet then I would love to see them. Can't see the man ever getting beat. I will never forget his fight with Hatton where he gave him a boxing lesson of all boxing lessons. Shame it doesn't look like we'll ever see him and Pacquiao but I reckon Floyd would do him.
Tiger Woods - had never knew much about golf until i'd heard of Tiger but even got me watching a little bit
Lance Armstrong - not a cycling fan but his record speaks for its self.
AP McCoy - champion jockey on so many occasions takes massive commitment and dedication especially with all the knocks and falls. not my most favourite jockey personally, but as a sportsman he is right at the top.

Mentions to:
Frankie Dettori - gave horse racing a lot of excellent publicity and attracted a lot of new people to the sport over the years, and winning every race at one of the meetings at Royal Ascot one year aint bad either.
Stephen Hendry - miserable bugger but his record speaks for its self.
Usain Bolt - can only get better at such a young age which is frightening.
Alan Shearer - for his dedication to Newcastle United and scoring so many goals for a mediocre team.

wrong topic

Strange that Andy as I was born 12 years earlier but having thought about it for a while 4 of my 5 are the same as yours....

Floyd Mayweather - An absolute master at his trade. Difficult for me having been a huge Hatton fan who followed him for years and in the States many times, but feel absolutely priveleged to be able to say 'I was there' to see Mayweather beat Hatton that night. Definitely go down as the greatest sportsman (IMO) that I've seen in the flesh.

Phil Taylor - Doesn't really need an explaination...

Tiger Woods - As above....

AP McCoy - Passion, commitment, desire, ability etc, etc....second to none. A great ambassador for racing and under-rated by so many people both inside and outside of the sport IMO.

Ian Botham - My sporting idol as I was growing up. Was a very keen cricketer when I was younger and I always wanted to be like 'beefy'. Great, great player...

Jack Johnson
Michael Johnson
Phil Taylor
Zidane
Roberto Duran

I'm amazed it took someone so long to mention Tony McCoy very few people are dedicated to their job like he is, he has racked up the champion jockey titles year on year and after finally winning the Grand National it puts him up their as the greatest ever IMO.

In no particular order:

AP McCoy
Phil Taylor
Tiger Woods
Lance Armstrong
Diego Maradona

Me too, thought somebody would of already mentioned him.

If he was in a more popular sport he would be umpteen time Sports Personality winner too.

I backed something else in the race, but when I noticed mine wasn't going to be fighting for the win I was willing McCoy to get Don't Push It over the line to get that monkey off his back.

From my lifetime, in no particular order:

In individual sports -

Jack Nicklaus
Tony McCoy
Phil Taylor
Manny Pacquiao
John McEnroe

In team sports -

Muttiah Muralitharan
Andrew Johns
Michel Platini
Viv Richards
Diego Maradona

Yes I know that's ten

Tiger Woods- Best at his sport for all of his career (so far)
Phil Taylor- As above just amazing and seemingly continues to get better and better
Tom Brady- Started as a nobody who "wasnt good enough", took his small oppurtunity and has gone on to become one of the best ever
Seve Ballesteros- Made up shots that nobody else would ever think of playing and made them look easy
Lance Armstrong- What else can you say about the man that hasnt been said

Can only say for the sports I follow. In no particular order.

George Best
Valentino Rossi
Phil Taylor
Mohammed Ali
Bion Borg

Have to say when I put mine it was a toss up between Borg and Mc Enroe.