I think one of the hardest things about apartment living is finding enough space to store your things. At least in the apartments I've lived in (and the ones my friends have lived in), it seems like there's just never enough closet space or shelving to hold the things that get collected over a year or two or three of just living. Someone gives you something, and it's great, but where on earth are you going to put it? Bookshelves are surprisingly expensive and it's tough to find the time to actually make something.
But I did find a project on Craftynest.com that looks like it would be a doable weekend project for not too much money--and you get a great bookshelf at the end!
This set of modular shelves was made from a salvaged pile of mismatched drawers that were painted, papered, and affixed to the wall with screws. Depending on where you find the drawers (you might even get lucky and pick something up on Freecycle), you can get pretty varied results, I think--all the same size, or, as in this photo from the Craftynest project, various sizes and shapes that are joined together by color.
As soon as I find some drawers, I'm definitely giving this a shot. We have an entire room worth of stuff that is simply sitting in boxes because we don't have shelves to put it on.
Link to the full project instructions is here.