So what other books are there like that, written over 50 years ago but still setting the standard in their field? The first one that comes to mind is The Joy of Cooking, originally written in 1936 (and revised a few times since then), it
continues to be one of our top 5 cookbooks every year, year in and year out, no matter what other cookbooks come along and catch the public's fancy and sell well for a while and then disappear.
Another candidate would be Strunk and White's The Elements of Style. This one is from 1918, and though other usage guides have come and gone, nobody seems to have said it as well as these boys.
My last candidate is a bit more obscure- Calculus Made Easy (as if). While we don't sell nearly as many copies of this as we do of the above-mentioned books, it still sells a few copies every year, exactly 100 years after it was originally published.
I'm not saying these are the best books in their respective categories. It's just that, for whatever reason, they have caught the book-buying public's fancy. Friends recommend them to friends, generation upon generation. Can anyone think of other books that fall into this category?