I am having such a hard time finding Stuff to put on my walls. I love my bedroom but my living room should definitely be qualified as a 'work in progress'. Yesterday I found the greatest website from which you can order the underground signs from Boston & New York (they are going to add Chicago very soon as well). I lived in Boston for a year and the T (that's how they call their subways) is the cutest underground/aboveground system I have ever been in, and I cannot wait to have a reminder of that on one of my walls. Btw, I think it's also an awesome gift to give someone who used to live in one of those cities and moved.
Also, You can even create you own!
They have different sizes: 12'x12' (30cm x 30cm), 58'x12' (147cm x 30cm), 94'x12' (239cm x 30cm)