I've been playing around with cold brew as well. Back in my coffee days I'd drink strong black coffee from Dunkin Donuts, but then they went more towards the Starbucks style brew and I lost interest. I'd occasionally drink with friends but had to add cream and sugar to make it taste ok and by that point I might as well just have a soda.
I've just been using Seattle's Best beans for now, it was all that Fred Meyers had for a dark roast at the time, and it's been ok. It is decent with 12-24hrs brew time, but much more than that it starts getting a burnt taste. It really grosses my wife out that I drink it black, especially when I add some salt to smooth it out a bit.