FBI: Here are your options. Door number one you go to prison for a very long time, door number two you help us get back the declaration from Ian, and you'll still go to prison for a very long time, but you'll feel good inside.
Ben Gates: Is there a door that doesn't lead to prision?
FBI: Someone's gotta go to prison, Ben.
As Ben is clinging to the staircase while it is falling apart, there is a close-up of a nail being pulled out of the wood. This nail is round-headed, rather than square as it would have been over 200 years ago. It's also shiny instead of rusty, which indicates that it's galvanized. Galvanization as an industrial, metal-preservation process was not patented until 1837, and was not used in building materials until well into the late-1800s. Since the film states the staircase was made by "the Founding Fathers, " and there was no galvanization of iron nails in any industrialized nation in 1780s-1830's, this is a huge anachronism.
When Ben is talking to Riley in front of the Lincoln Memorial, you see a long pool behind them. This pool is filled with computer generated water, because the pool was drained at the time of shooting.