Step 1: Shooting
1. Ideal shooting position is halfway between the top and bottom of the building (or area of the building). This, of course, requires a ladder, or shooting from the building across the street. Horizontal position is obviously directly opposite the middle of the building, which is often helpfully marked with a door or window. A ladder isn't necessary if you have a Tilt/Shift lens (24mm" works well in many situations), but these lenses are expensive, and aren't available for all lines of SLRs (Canon has a good one, but it's $1100+). TS lenses straighten the converging lines effect that you get if you shoot up at the building from the sidewalk across the street-- you can do a lot of the same thing in Photoshop (see editing step.)
2. Hold the camera with the image plane (back of the camera) exactly parallel to the building. This is tricky and takes some practice. On a positive note, you don't have to hold it perfectly still, because the building is happy to sit still for you.
3. Often, a picture is a bit more exciting if someone is walking by, or if there is an object to grab the eye in front of the building. In the picture illustrating this step, the lamp-post adds a little something extra. If you're going for something in the foreground, make sure to use a smallish F-stop to keep the depth of field deep (F8 or above usually works fine from across the street). This way everything will be in focus.
4. Avoid any distracting elements-- that include:
-- lampposts (almost never look good unless they are at the edges, and then only if they are distinctive)
-- cars (death to most photographs because they destroy that "what year is it?" quality, and tend to block the front of buildings)
-- strange things in the background or foreground, like wires or satelite dishes
5. A word on lighting: buildings always look best an hour before sunset or an hour after dawn, and generally look better on slightly cloudy days. Bright light, particularly in the afternoon, will cast harsh shadows that make buildings look bad. Avoid shooting at noon at all costs. Avoid any shot where you can see clearly delineated shadows, unless they really work.