The evangelical magazine Christianity Today asked three people, "What classic spiritual discipline needs the most renewal among American Christians?" Dallas Willard, whom I admire, said "Silence," which is a very good answer. "Fasting" was another suggestion with which I sympathize; on the other hand, "Listening to Jesus" through isolated Bible verses in private prayer without any structures of hermeneutical or ecclesial accountability seems to me to feed directly into our main problems as American Christians (and it's also not a classic spiritual discipline, but I'll leave that aside).
What I cannot believe is that nobody said Self-Denial. Can there be anything we need more? When I suggest tiny acts of self-denial to Christian groups (leave the heater in your car off for 5 minutes, let one subway train pass you by before you get on, set aside a bite of your meal), the stunned, uncomprehending reactions are so striking that I kind of wish I had a photographer to capture them, so that we could make a conceptual art piece out of it one day.
Or how about the discipline of going to church every single Sunday with people dissimilar to you in age, wealth, politics, and education to attend services that are not designed to be to your taste? (There's not a name for that one, but I'd argue it's classic, all right.)