I've had great results with a coffee porter by just adding about 16 ounces of strong, fresh-brewed coffee (I did French press, but probably doesn't matter much) when racking to secondary. Nice, subtle coffee flavor that way- you know it's there, but it doesn't smack you upside the head.
That being said, there are plenty of different ways to add coffee to a brew, and people seem to have good results with all of them. Just experiment and see how it comes out... but be sure to let us know the results!
You can't be a real country unless you have a beer and an airline. It helps if you have some kind of a football team, or some nuclear weapons, but at the very least you need a beer. -Frank Zappa