Silas and the alphabet puzzle
When we went out east, we bought an alphabet puzzle so that Silas and Russell could spend a few days learning how to put it all together. On the first or second day we were at the beach, I pulled out the puzzle for them; Silas and I were staying in the beachhouse for a while, and he wanted something to do. He needed my help once (to pull the H out from the space for the N, and then to tell him how to rearrange the H so it was rightside up), then played happily with it for a while until he decided to go down to the water.
The next day, Julie decided to help him do the puzzle, and discovered that he didn't actually need any help, because he was putting the puzzle together all by timeself. Later that day, Julie's mother was trying to help Silas, but ended up watching in amazement as he put the puzzle together in no time flat.
The next time Silas did the puzzle, I had the camera at the ready and filmed a movie of him doing the last 2/3rds of the puzzle (WARNING: this is a 48 megabyte .avi file that lasts about two minutes). Note that this is the fourth time Silas did the puzzle, and he'd never seen it before the first time he did it. Note also that he's just over two years old.