I came across this one a year ago and mentioned it on my personal facebook page, but it is definitely worth repeating.
Imagine a 6.65 acre American flag made out of flowers?
It was 740 feet wide and 390 feet high and contained over 2 million flowers! It was created in Lompoc CA. back in 2002. Aerial photo courtesy of Bill Morson. Truely amazing!
http://www.stumbleupon.com/su/1Kqevb/www.sjcaravello.com/flag.html