Favorites in our house...
Legos, Duplos, Quatros. Blocks always get used. They also like wooden blocks.
Little People. They especially love the barn and the big car ramp/parking garage.
Marble race. Like, a big plastic structure you build and then drop marbles in the top and watch them go down all these different gadgets...that thing has seen a TON of play time.
Mine personally didn't love their dollhouse. A very nice dollhouse, tons of really nice furniture and fun accessories (all old style, not Melissa and Doug style...so, the phone actually looks like a little phone, there's a little knitting basket with tiny needles, a toaster made of stainless steel that really pops up tiny tiny pieces of toast, mahogany looking REAL looking furniture...) and they don't play with it!!! I played with my dollhouse a LOT...my children don't. Oh well.
Lincoln Logs.