Ds has the fire engine (not the station just the big engine) and the police station with the van. He loves them both and they get played with a lot. Apparently dd is getting the zoo for Christmas or birthday from the same uncle who got the others for ds.
Oh just remembered, ds has the digger with the builders too The digger is good value, you can take the top off and build on to the base to make a tank
I've never bought a big set of duplo, I just buy smaller sets and boxes of bricks second hand, that makes it far more interesting and the children can use their imagination. The link MrsJammi has posted looks interesting, we have many of those pieces - the winnie the Pooh set, zoo animals, slides, trains.