To talk anymore about Helvetica seems pretty awkward. There is now even a movie with Interviews to important designers, featuring David Carson, Erik Spiekermann, Matthew Carter, Massimo Vignelli, Wim Crouwel (availlable in DVD and Blu-ray). In the movie you will find a lot of the theories that I find most intresting and write about in my lessons on how to become an art director. Besides the admiration to this great font we find it difficult to find alternatives. Maybe - but I've found a quite some very cool fonts, that can take on the ultra classic font Helvetica.
from Linotype (www.linotype.com) The links next to the fonts are linked to the example pages of the foundry.