The two lions seen on either side of the steps down from the elevator to the secret library are not duplicates of the two lions, popularly known as Patience and Fortitude, outside the New York Public Library. Rather they are copies of the lions on the monument to Pope Clement VII in St. Peter's Basilica, Rome. They were sculpted by Antonio Canova between 1783 and 1792.
The Artifacts in the Library are: Tesla's Death Ray, The Holy Grail, Little Boy (atomic bomb), The Ark of the Covenant, The Golden Fleece, King Midas, Excalibur, the Goose that laid the golden egg, Pandora's Box, the real Mona Lisa (a copy is in the Louvre), a Unicorn, the Rocketeer's Jetpack, Ali Baba's Flying Carpet, and the Spear of Longinus (Spear of Destiny).
In the jungle when Flynn reads Nicole's (played by Sonya Walger) personality, he says among other things that her father is Argentinian but that she never learned Spanish. Sonya Walger's Father is actually Argentinian however contrary to the film she is fluent in Spanish.
When the elevator doors open and close at the bottom of the library, the sound made by the Turbolift doors from Star Trek (TOS) is heard.
Flynn, looking from the jungle tree top, figures their position is -5.2° latitude and -64.6° longitude. Minus latitude means just south of the equator; minus longitude means west of the prime meridian, which goes through Greenwich, England. A position -5.2 lat. and -64.6 long. is in the Amazon Basin.