Hi A. -
You got a lot of great responses and it looks like you may have found the answer! But, we went and still go through bouts of night wakings with my 20-month old son. They are tough on you and them!
Just an FYI for the future of something you MAY want to try (though every baby responds well to different techniques!).. We were not cry-it-out people, so when we knew my son was healthy and it wasn't a sickness, tooth etc., we have really good luck doing pick up/put down as suggested by the Bbay Whisperer. We would go in and pick up and hold him only until he was calm. THe moment he was calm, we would set him back in his crib. Even if he started crying on the way down, we would complete the put down and pick him up again immediately if he was crying. We would do this until he could lay him down and he was calm. It worked well with our son and he would cry a little, but we never left him alone to cry. We always comforted him and reassured him right away, but it also encouraged him to self sooth.
Obviosuly this is NOT a good technique to use when a child is sick or in pain, but if you have ruled those out, it might help you! It can take a little while to get them back to sleep and it may last for a few days or a week, but it worked for us and him!
Good luck.