I would suggest one of 2 things, but depending on your parenting ways you might not like them it's not for everybody. Firstly have you tried sitting with him for a while until he settles? I don't mean literally sitting with him but perhaps on the other side of the room just so he knows you are there. He will probably still cry for you a bit but you can gradually pull yourself further back as he gets usd to the idea. Start the first time by stroking him softly and sitting quite close, then next time do it at arms length, then slowly further away each time. Like I said it's not for everyone because at some point it probably will mean leaving him to cry a little while he tries to understand what's going on, but after just a couple of days he should settle quicker and quicker.
The other thing is very similar although a little more harsh, and someone else has already mentioned it but try controlled crying. This means you put him down in the cot and walk away. He will almost inevitably cry for you but leave him a couple of minutes then check on him and reassure him before leaving again. Then gradually leave it longer and longer before going to check on him. It is VERY hard to hear them crying and can be difficult to not respond but believe me, it will work. Eventually he will get so tired that he will fall asleep totally exhausted. I was never very keen on either idea when they were suggested to me, but when you get desperate for some sleep you will try anything! Both methods have worked extremely well for us, and we've only ever had to do it for a few days on one occasion and our son learned from it very quickly.
