I find some of Woody's songs quite timeless. "This Land is Your Land" is obvious, but, just because a song has historic context ("So Long, It's Been Good to Know Ya") wouldn't disqualify its timelessness in my book. 'Course, that's just my book. Hoagy wrote a lot of love songs -- I guess those are timeless by definition, but they generally don't appeal to moi.
Spaw speaks of the crazy lists people come up with. Reminds me of the "100 Most Important People" of the past 1000 years A&E came up with. Oh well, at least they got #1 right. (IMHO)