Moleskine City Notebooks

I bought the Moleskine City Notebook last year and I highly recommend these for city travel. They make them for every city. It has all the maps you'll need, including subway. Plus it's small so you can use it while you walk around without feeling like you're holding a giant sign that says, "Hi! I'm foreign! Please rob me!" 

It also has transparent sheets that stick over the maps like a big post-it note, which allows you to write notes on the maps without ruining them... 

And like all Moleskine notebooks, it also has plenty of pages for notes and drawing, as well as pockets to stash stuff.