I'm not a baseball expert by any means, but I'm pretty comfortable in saying:
Hitters: Babe Ruth, Ty Cobb, Ted Williams, Joe DiMaggio
Pitchers: Walter Johnson, Cy Young, Nolan Ryan, Sandy Koufax
For pitchers, I feel Walter Johnson is really outstanding. If you read about him, you'll see why. I kinda don't like that all the great hitters are from eras past, but they are definitely ranked as better than modern-day hitters by experts. A part of my insides tugs at me and says that "modern hitters have it way tougher because they constantly face fresher arms". In the past, a starter often finished the game. Nowadays, there's middle-relief, set-up man, and closer - things that didn't exist way back when. Plus, there's specialist pitchers "made" to go up against certain hitters.
Derek Jeter is not a top 10 guy. Shaq might be a top 10 guy for peak dominance (in fact he almost surely is), but he could be squeezed out of a top 10 careers discussion. Tom Brady is most definitely a top 10 all-time quarterback - see debates between him and Peyton Manning on football forums, etc.
For individual sports: Jahangir Khan in squash, Edwin Moses in 400m hurdles (unbeaten for a decade), Aleksandr Karelin of Greco-Roman Wrestling, Sonja Henie of women's figure skating. All of these people are worth a read in your spare time.