Have you tried Legos yet? My younger son started putting together Lego Technics when he was 15 months old. I wouldn't have dreamed of introducing them to my older son at that age but when my younger son saw his big brother playing with them he wouldn't stay away. He developed amazing fine motor skills and spends hours playing with them. He likes the Duplos, too, but both of my kids prefer the Technics because they like all the moving parts.
Like the poster above, I have found that puzzles have not been a good purchase for us. The kids put it together once and then move on. I'd recommend more open ended building toys. Some that got a lot of play at our house at that stage include blocks, magnatiles and, closer to two, marble runs, Quercetti tubation sets(simple pipes that you can build with, one of our best purchases ever), and Jawbones. These building toys have all lasted years and through many stages. When your kid gets sick of a set, put it away and take it out a month later and he will be captivated for several days again. If you have a kid who tends to put things in their mouths, marbles aren't ideal but my kids never did that and after watching them closely for several months I was satisfied that they could play with them safely.
