I also like "I was happy to do it," especially when your kind act could have been interpreted as obligatory. A version of "No problem" is a common European response: di niente, de nada, de rien, etc., but "it was nothing" is closer and sounds nicer to me. If you spend hours and hours making a quilt for someone, they thank you profusely and you say, "It was nothing" someone had better let them know it was indeed something so they don't treat it like an acrylic blanket from Walmart.
