>>213362855 (OP)
Well, American Beauty got all the awards. It represents the I Hate Work Angst of 1999 well, alongside it's fellow 1999 releases Fight Club and Office Space. On the other hand The Matrix has probably had the longest and strongest influence. The one that most accurately reflects the actual era is definitely American Pie (granted, I was a teenager, so that probably helps).
I think Magnolia best represents that year and period of filmmaking itself thoughever - An insanely technically accomplished film with a big budget and movie stars...that is a 3 hour long quasi musical drama about emotionally retarded losers. It reflects just how different Hollywood then and now is.