There are less and less options out there for play sets. As toy companies cut back due to cost cutting options, you have really no other choice than to make your own stuff or look elsewhere. Some people use Imaginext and Playmobil. Those items are not quite in scale with a typical 4" figure, but they work. Other people just use styrofoam like when they were kids.
Now there is a new option. With D&J Toys, we mostly push the display abilities. A way to put your figures in an environment to show them off. These items still will push a display idea, but there is also a play element to them. Much like the Cobra Missile Headquarters, there are interactive features. The idea is to bring in some fun into your display. Some of the sets can be placed next to each other to give an idea of expanding the fun.