This is the kind of thread that a few short months ago I would have looked at and thought "what, discussion of the day, must be a slow day on MN" but having had a recent renaissance in terms of decluttering, I now can answer this question in exquisite and painstaking detail!
Kitchen - we have a 50's style pantry and in it we have an Ikea duktig kitchen that houses: playdough, baking equipment, "cleaning" equipment (and some real cleaning stuff for ds to help out in kitchen with), toy food, a toy kettle/toaster/kitchen utensils. We also made a bench using an Ikea storage thingy and it houses the arts and crafts and jigsaws as I don't want the kids getting into these on their own because they throw paint everywhere and lose all the jigsaw pieces need some supervision with them.
Lounge - We have a trofast storage thingy from Ikea. This used to have tubs of toys in it but we have stripped it way back and put in shelves so there are now five or six books, an Octopod, duplo, some stacking cups, rattles and a shape sorter. When the kids go to bed, we throw a table clothover it and it functions as a coffee table and we can pretend that the room is kiddy free.
Bathroom - Bath toys, of course!
Boys' room - we converted their wardrobe which was a built in when we bought the house into a reading nook. It was a really odd shape, deep and very wide but with small doors so it was very hard to get into the corners, so we built in some shelves ourselves by hacking some ikea storage. When you open the door, you can see a blanket hanging on the wall and some arty farty bits decorative features 
, giant cushions and a cosy fleecy blanket with stars on it that is hanging from a Grundtal rail. To the sides there is a trofast hacked storage shelf with animals, bricks, vehicles, musical instruments, puppets and "little men" (e.g. firemen sam and the like). On the other side there are book shelves. Up high there are flexible buckets with more flashy toys in that don't come down everyday but are great for when you need a break! We have two night lights in there and chalkboard paint on the door and a hung abacus so they can draw on the doors. Big hit. We call it the "play and read" nook.
Finally, we have an expedit (four bits) between the beds. This is empty and they can make things with bricks etc on it - my 3 year old makes it into a shop, a castle, a hospital etc. I got the idea on Pinterest, as I did most of these ideas!