I have had the same problem with my son... twice. When he was about 16 months it started and only lasted a week or so I think. He worked through it and I followed his lead. I met his needs, comforted him, but didn't take him out of the crib.
We are going through it again. It started with cutting four teeth, then the holidays, then a trip out of town, then shots. It was about 6 weeks of chaos for him. We were back at square one. I am adamately against CIO. I believe that we have to give our kids a voice. There have been many nights during all that that I slept in his room on the floor while he held my hand through the crib.
Here is what I did (do) and it is working...
I nurse him before bed and put him down. When he wakes up several hours later he nurses briefly and I put him back. He always wakes up at this time now. I comfort him and tell him it is ok to go to sleep and I love him. He doesn't lay down. I say "mommy is very tired. I love you, but I am going to go lay down and I will be back when you are ready to lay down too." I leave, he cries. I only stay gone for a minute or so and then go in and tell him to lay down. He does without a fight and I rub his back for a second and then just stay there with him until he is sleeping. He is getting better each night, less crying, less fighting.
I think the important part is that i am answering his cries, I am giving him a voice. But I am setting some limits. He is 19.5 months old by the way.