Washingtoniana Room or other archives, you know they are GREAT! All hand colored, they show what was on each Square in 1887, with brick houses in red and frame houses in yellow.
They also show lots of other cool stuff, like streams running through the Square (that would explain why your basement always seems damp), horse drinking troughs, sewer lines, and even what type of paving (or not) your street had that year. We purchased a complete set of these maps from the Historical Society Book Sale about 15 years ago (they often sell duplicates, not to worry) and had them scanned in real size (they measure an impressive 2 by 3 feet or so) at 400 dpi for our own use so as to not damage the originals during our research.
Update 2/20/12: all original maps have sold!
I've enjoyed bringing the maps to the masses via excellent quality prints that we also sell on eBay. You can order any of the 44 maps in all, and they make for a great piece of interesting wall art. I'll link you to the popular Dupont Circle map HERE to get you started.
Feel free to ask me to research which map your house or building might be located on, and I'm happy to point you to the correct map. They are quite the conversation starter, and you'll find yourself quickly immersed in their detail.