As convenient as it is to just run into Starbucks to get your quick caffeine fix (because there is one on every corner downtown), it can be much more rewarding - and delicious - to try other places that are a little less famous.
My favorite cafe happens to only be 5 blocks from my house. It's called "N Street Cafe"... and it's on N St. between 20th and 21st. Not only do they have yummy lattes, they make a (vegan) falafel pita that's to die for. I get my pita with their cilantro jalapeno hummus, which they make there, and it's pretty much the best thing I've ever had.
They also have tea, smoothies, sandwiches, salads, and fruit, so even if you don't like coffee, you can find something tasty to eat/drink. And there's free WiFi!
Here's a link to a site with their address, hours, phone number, and some reviews.