Although its trendy to hate Starbucks they do have pretty good coffee for a large chain provided you like dark-roast or at least potent brew. (anything other then standard brewed coffee not so much IMO)
Also at least in my area the price is within 15-20 cents of Dunkin as well ... having said that when I buy coffee on the road its $1 Cumberland farms whenever possible cheapskate that I am!
Edit: For those not familiar with Connecticut/New England Cumberland Farms = Circle K, 7-11, Krausers, Wawa etc