I could spend all day browsing around Google Books.
Today I came upon a 1581 edition of the very first Hebrew concordance, Meir Netiv, written by Yitzchak Natan (Isaac Nathan) ben Kalonymous in 1447.
It is interesting because of why he wrote it.
He was heavily involved in arguing against Christian missionaries to the Jews and Jewish apostates. They would quote chapter and verse for their arguments, but Jews couldn't easily answer them - because the division into chapters and verses were a Christian innovation!
Isaac Nathan therefore wrote the first Hebrew concordance of Tanach to aid Jews in arguing back (and exposing fake quotes that Christians at the time would use.) This was one of the first Jewish publications that used the Christian chapter and verse system.
Another innovation was that this concordance alphabetized the Hebrew words by their root word, so it was easier to find a specific word.
If you want to find all Torah commentaries in Google Books written before 1600, click here.