I currently have two large (50ltr) lidded boxes that contain terrain and other bulky items. One holds 28mm scenery for roleplaying games while the other is now dedicated to my growing collection of 15mm terrain. Because of their size these are stored in my bedroom on top of my wardrobe. I also have four Games Workshop storage cases holding a growing selection of models for roleplaying.
In addition to these cases I have an aluminium model case that I bought for my Flames of War miniatures. It comfortably holds all of these and there is plenty of room for new models (especially at the speed I paint). Then there are several boxes of magazines and hundreds of books. Most of this is in the Living room - on, around, and under my computer desk. It's not exactly tidy but it is all in once place...sort of.
I'd love to have my own game room but until I chuck my kids out I guess I'll have to wait. In the meantime I decided to have a good sort out. A few month ago I got rid of a load of gaming books, supplements and magazines. My mate put these on EBay for me and most of it seems to have sold quite well. I have also reorganised where I store stuff, clearing some space in my bedroom cupboard for boxes. Its still not ideal but at least its out of sight and isn't cluttering up the family room.
Another longer term option is outside storage. I have a brick built shed in the garden but the roof collapsed a few years ago and I keep putting off rebuilding it. If I can make my shed weather proof again then many of our storage problems would be solved. A few large plastic boxes, suitable sealed could be used to store all manner of items outside the house. So, instead of painting this weekend, I'll be dodging rain showers to remove whats left of the old shed roof and clearing the inside of rubbish. I'd rather be painting, but I have to think of this a long term strategy to get a dedicated gaming area inside the house.