For my money, Thor: God of Thunder is the best book of the relaunch. Just fantastic, ambitious, epic stuff with gorgeous artwork.
I also really loved Captain America, though your mileage may vary depending on your feelings regarding John Romita Jr. I really liked it though, as it's very fresh and very different, sort of Steve Rogers by way of John Carter.
It's not Marvel NOW, but you should also give Hawkeye a try. I firmly believe that it is the best book Marvel is putting out right now and one that everyone should at least try.
It's not out yet, but I'd also keep an eye out for New Avengers. It's Jonathan Hickman writing the Illuminati, so it's bound to be a cracker.