I too would also have to separate the Fabs from the rest.It's hard enough trying to pick just THEIR best one let alone the greatest or most influential of the entire imagination fueled 1960's.Beatls included and considering general notoriety,most would agree "Sgt. Pepper" was the decades greatest recorded sound triumph.Among all other artists(or even including the Beatles)Velvet Underground's debut is a strong candidate here,especially weighing in the factor that it was so ahead of its time,its full influence was partial cause to the Grunge movement of the 90's.Lyrically,perhaps Dylan's "Blonde On Blonde" or "Highway 61 Revisited" is master of this domain.Certainly highly honorable mention goes to "Pet Sounds","The Doors" "Are You Experienced" and LOVE'S timelessly charming "Forever Changes".But the single greatest?Too many high artistic achievement on too many levels to truly come to a call here.What a cop out,huh?!