All you need are two fonts each from four classifications of sans serif fonts:
Grotesque: Frankling Gothic, Akzidenz-Grotesk
Humanist: Gill Sans, Frutiger
Geometrical: Futura, Avant Garde
Neo-Groteque: Helvetica, Univers
I would also throw in:
Impact (Neo-Grotesque; a better display font than a text font)
Optima (considered a humanist letter style, really useful for medical and cosmetics)
Massimo Vignelli once wrote, "In the new computer age the proliferation of typefaces and type manipulations represents a new level of visual pollution threatening our culture. Out of thousands of typefaces, all we need are a few basic ones, and trash the rest." He preferred Helvetica, and Akzidenz-Grotesk, (sans serif), and Century Expanded and Garamond No. 3 (serif). Throw in Futura and Bodoni (probably his signature typeface) and you essentially have this influential designers complete font collection!