Studying history is great, but when you can actually see something you have lived through, that is even better than great.
In my never ending quest to see everything in NYC, I took the F train to Brooklyn, a borough I barely know, and paid a visit to the Transit Museum. Actually seeing the engineering and labor that went into creating this system was phenomenal and then actually going into the old trains, trains I remember riding, was fantastic. But, the best part was the advertisements on the walls of each car. The quality of the pictures are not so great (my camera is still in the shop and I accidentally turned the flash off on my little point and shoot) but they are still worth seeing. (Pictures here.)
For anyone in the NY area, don't wait as long as I did to visit this fantastic museum. Only one problem--it is underground and there is no air conditioning--kind of like the old days of riding the subway.