Mega Blocks are great aren't they - as well as the stacking/nest variety of blocks that Lucy mentioned. Jacob has both of these and has an absolute riot with them. Wooden peg-style puzzles are good, as are shape-sorters.

Jacob also has a baby doll that he plays with and he loves it. I've also seen him playing with some of his little friends toy cooking things and he thinks they are great too!

We also found that about that age Jacob was starting to enjoy drawing and stuff, so big crayons/markers/pencils that are easy to hold are great (just the action of taking the lids on and off the markers keeps him amused a lot of the time!), as well as blackboards etc to scribble on.......