I have a six-pack and it has been a bitch to get and maintain. I usually work my stomach every day. At the YMCA, I do three sets of 80, 90, and 100 lbs until I can't do any more. At home, I usually do 2 sets of sit-ups (ish) and 2 sets of this pilates exercise. I don't eat a lot, but what I do eat is healthy. I don't eat ANY junk food. Keep in mind that everyone has a six-pack, but if you can't see it, it's covered by a layer of fat.
PhD student - Organic Chemistry
I don't read an entire thread before I respond; I try to answer the question quickly and concisely.