Ethan was really skittish, still is to a certain extent. He's been much better since we started giving him those kitty treats with the wheat grass in them. Not sure if you've seen them, but they carry them at chain stores like Petsmart and Petco. He LOVES them! I've also got my husband to stop pestering him and he was neutered last month so I think that's really helped.
My oldest cat is semi-feral and still nervous after many years. It is important to recognise where their weaknesses lie. She is really neurotic about the bin collections so we always make sure that she can get into either the house or the garage on collection days, etc.. She has grown immensely in confidence over the years but is never going to be as laid back as some of the others. She shows us loads of affection and loves us so we live with the problems.
Have you tried a Feliway diffuser or calming treats from Pet Naturals of Vermont? I've seen that they are recommended on a lot of other posts for mellowing kitties out, whether they're nervous or aggressive.