I cheated and bought a kit. I want you to know that up front before wondering how in the world we found such beautiful samples, etc. etc.
I bought the one from Home Science Tools. Here's a linky: http://www.hometrainingtools.com/tree-leaf-identification-kit/p/BE-TREEKIT/
I don't know if it is worth the price for you people who can actually look at a leaf and figure out what sort of tree might have produced such a leaf. As I've said so many times before, I am not a scientist. I put up with science because it is my children's favorite subject. I am also not a naturalist. I love being outdoors and take my kids hiking two or three times a week three seasons of the year, but I still can't tell you the names of anything that we see (except when we run into moose--even I know what a moose is).
My point is that the kit was worth the money to me because it made my life easier. We made a fun poster, the kids loved looking through the identification guide, we justified two or three hikes by gathering leaves, and in short--we had a lot of fun with the kit. We also tried to dry leaves and make pictures out of them but we waited a hair too long and the leaves were all a little too dry and brittle. Next spring, summer, and fall we plan to try again.