Almost everyone collects something, whether it's books, baseball cards, old 45rpms or (heaven forbid) pieces of burned toast with Elvis' face on them. The trouble with collecting actual things of course, is that things take lots of room. I collect photography books, for example, and trust me, pretty soon either some of the books are going to have to go or I'm going to have to add on another room.
But one way to collect things without actually storing them is just to photograph them. Then you can have a collection of something and it won't take up any room at all. Also, by just collecting pictures of neat stuff it's much cheaper and you can also collect stuff that you can't necessarily run into a store and buy. I started collecting photos of unusual manhole covers, for instance (like this one that I found in Paris near the Eiffel Tower) and I've discovered that there are some really interesting and unusual manhole covers out there. I even found that the ones on my street have the town name and the year they were installed engraved on them. Cool! But even if there was someone selling them, I'm not about to start hauling them home.
As with all collections, the stranger or more esoteric the object is, the more fun it is to collect (and the more eccentric your friends will think you are). Then once you have an interesting collection going you can print pictures of your prize possessions and the only room it will take up is a photo album or two.
By the way, you won't be the only person collecting whatever sorts of odd stuff you collect photos of because I guarantee someone else is collecting it too! How do I know? A few days after I posted this shot of the manhole cover on my Flickr photostream someone invited me to add it to their group of...you guessed it, manhole cover photos.