Construction toys such as Legos and K’Nex are great for keeping kids busy. There are sets for many ages and interests. My own favorites are the basic sets where you aren’t trying to build something according to package instructions, but my oldest daughter loves following instructions to build neat stuff. She also builds just on her own, of course.
Mess control is key. I’ve heard it said that all Legos are created equal – they all hurt the same when you step on them in the dark – and it’s so true. Don’t let these toys get into places where you’re always going to be stepping on them.