Is Landa's Giro the greastest appearance on a GT...

In recent years:
Rujano: 2005 Giro
Gutierrez Cataluna: 2006 Giro (although not a real challenge to RoboBasso)
Peter Velits: 2010 Vuelta
Kaschechkin: 2006 Vuelta
Pereiro Sio: 2006 Tour (mostly luck on his part).

Ofcourse Froome tops all of the above examples, as he litterally came out of nowhere in 2011.