In our space, we decided to turn our eat-in-kitchen into an office (pictured at top). We used our wine bar turned kitchen prep table also into an office desk/bookcase. We simply took out the wineracks to create a bookcase. This one piece of furniture offers tons of uses plus it's sleek and compact. Another great bar (and currently on sale) is the Liam Bar at World Market.
Also check out The Container Store's elfa units. Incredibly functional and available in a range of options, make your own office as big or small was you want or need. I also love the idea of creating a home office out of bookshelves. I found this concealed office idea in Martha Stewart Living. Check out instructions to make your own here.