Most of the time, when you visit someones house,apartment, or whatever, you'll notice DVD's,CD's,action figures,books, or something to that degree that people collect and either show off or not.
Myself, i collect plastic gundam models, like the one showed here:
Sure, some people think they're a waste of money, and even time. But i like to build and sometimes paint these models. It occupies time that i would spend braindead sitting on the computer,watching tv, or playing a video game.
As of now i have around 20 gundam models, and one Ingram from patlabor sitting on a shelf completed. Its a costly hobby, with most running in the 20-120 dollar range, but they're neat to show off when there finished.
I used to collect baseball cards and the like, but i ended up with two big boxes full of them.