Re: Who do you think will take over tennis along with Sharapova in the future?
Sharapova looks the most consistent of the "young" players (I'm starting at twenty two and going down). I'd say start looking at Kuznetsova and Jankovic to be making waves on the slam scene, semis, finals, wins (?) next year. Both of them have the one element that Sharapova lacks: movement.
As for challengers, I'd say Golovin in two years will be really dangerous, as will Peer on clay, Krajicek looks better each tournament she plays (dangerous serve for a vertically challenged player, no?). Sharapova may be the hottest player on tour at the moment, but she still has issues on clay. It's also valid to point out that Hingis probably has another 5 years in her. If there's one thing a prolonged break from tennis is good for is increasing life expectancy. See Graf, Steffi; Evert, Chris; Borg, Bjorn. Plus, it's not as though the Williams' sisters can ever be counted out of a tournament. Henin's not dead yet, Mauresmo is still the best grass court player on tour IMO, and there's a whole host of Sharapova clones who just haven't got the creepy intensity, all capable of beating her on their day.
I doubt tennis will have a singular driving force for a while. If they do, I'd imagine they need better mobility than Sharapova. Can you think of a player with worse overall movement to be #1? Davenport had front to back, not side to side, but Sharapova has neither. She's at least solid now, but when she was #1, she was SLOW for the top ten.