My favorite brand is Green Mountain. Most of the places locally only sell it in k-cup form, but you can get bags of it online. For someone who wants a milder coffee, I'd try either Breakfast Blend or Nantucket Blend; I know the Breakfast Blend comes in decaf. (They have flavored coffees too, if you like that sort of thing, and they are SO GOOD. Not sure what's available in decaf, but I've seen a half-caff vanilla.)
I personally really, really love Columbian roast too, and it is pretty commonly found in decaf. But it might be a little bit stronger than the other two.