Dress ups - we have lots of very open-ended dressups - like large square scarves in lots of different fabrics - op shops are a good source for these. The nightwear section is great, we have a number of wacky old nighties and robes that get used in dozens of different ways.

Play-doh - we have zillions of different sorts of cutters & things - food-based ones are a huge hit (esp during masterchef season) but we also have a couple of sets themed around random things like fairytales and dinosaurs. I buy the play-doh instead of making it because i find it keeps well, and the kids have lots of colours to play with.

We also have a pretend kitchen with a variety of pretend food which gets used a lot - dolly tea parties, more masterchef, etc etc. I'm a bit fussy with this though, a lot of the pretend food is dang ugly, so I've only bought nice wooden sets or Target had a huge range of fabric ones a while back. The kitchen is stocked with a plastic tea set and then a whole lot of op-shop "real" kitchen stuff - wooden spoons, tea pot, etc.

Also, weirdly enough - we have hung onto our wooden block set and it's getting a great work out now that DD's a bit older - she plays a lot more laterally than she did when she was younger.

After mucking around with different storage options, I now keep the most used sets in those big stackable plastic drawers (got ours at Big W). The drawers pull all the way out so you can carry the whole drawer to the spot where you're playing, then put everything back in right there and the whole drawer goes away. Makes packing up easier. We keep all the little "critters" (eg pet shop, disney fairies, zoobles etc) together in their own seperate drawer - helps prevent them drifting through every single part of the house. Top tip for lego - have a lego quilt or mat so you can just pick up the corners and tip the whole thing into the lego container.