I have added coffee 2 ways to my beer.
I did a robust porter where I added 1 shot of fresh espresso into each (16oz) bottle and racked beer right on top of it. This gave a strong flavor of coffee, and a decent amount of aroma.
In my Mocha Mild at NHC, I used 1 qt of boiled and cooled water with 1/4 cup of coffee grounds, and cold-steeped for approximately 24hrs. I filtered this mixture through a paper towel and added it to the keg. This had a slightly more restrained coffee flavor, with less bitterness. I didn't get much aroma at all.
Also in my Mocha Mild at NHC, I took 1/2 cup of vodka and poured it over 1/4 cup of cocoa nibs. I let it soak for close to a week, and added it into the keg. With this treatment (and I think it would work with coffee as well) I got a strong cocoa smell, but with very little cocoa flavor, just enough to balance the coffee and give me the "mocha" flavor I was looking for.
My Mild at NHC got a lot of compliments, especially for a 2.6% ABV Beer.