roman kreuziger and robert gesink are already established GC riders, so the future's bright for these two hopefully and they're likely the best bet to challenge andy schleck and vincenzo nibali for the next 7 - 8 years.
there are also those who're nearly there but need some polishing like; (in no particular order)
bauke mollema,
richie porte,
robert kiserlovski,
tejay van garderen,
of course, those who climb well are definitely in there, which should include;
kevin seeldraeyers (best young rider in Giro09 is no easy feat)
romain sicard:
rigoberto uran,
rafael valls ferri,
dan martin,
ben hermans (if radioshack signed you to climb, then you're a good climber)
as for rein taarame and simon spilak, i think they're more into the damiano cunego mould, not a real GC contender but dangerously aggresive in hilly classics and 1-week races. or maybe they could be developed into another vinokourov, who can animate the race at will.
fabio felline? isn't he a sprinter?
hard to tell though, since in 5 to 8 year span of time there'll still be contador, jurgen van de broeck, igor anton, juan mauricio soler, who are all currently still around 27 to 28 years of age.