Have you tried homeopathy? I tried EVERYTHING with my DS and he was up in the small hours for hours sometimes. But those little pills are magic!

Other things that work for us:
sleepy classical music CDs
porridge before bedtime
taking time off - if I get stressed then DH can do it as I wind down and then I take over again... you have to be calm yourself and sometimes this is the only way to do it. Sometimes we both get stressed and DS has to cry for a few minutes while we recharge, but that's better than us screaming at him or hitting him or something similar.