I did some canvasing of the forum last month to add coffee to a Porter. I was given lots of methods. The one I decided on was to add whole beans to the fermenter.
I added 1 ounce of whole beans to 2.5 gallons 6 days before bottling. I was very surprised to find the sample tasted excellent at bottling. I have yet to have a bottle yet; I have one in the fridge cooling right now and will be trying it later.
From what I understand, steeping the coffee cold, draws the flavor as it it very soluble in water, but does not get the astringency you get from hot coffee, making for a smoother overall flavor. As I said I only had the hydrometer sample at bottling, but I was impressed.
EDIT: Just had the beer I mentioned. Tastes great, lots of coffee flavor. However, the beer also has Oak, Rum, Vanilla, and smoke. The coffee seems to be one of the dominant flavors coming thru.