Ah, the human pacifier...I remember those days well!
My son officially weaned HIMSELF at about 15 months so we didn't have major struggle. At the end he really only nursed a couple times a day, usually to go to sleep.
As I was "weaning" I started with nap time since that's when I have the most patience, trying to come up with other ways to get the kid to sleep. I found that rocking him worked. He'd cry and protest...but eventually he'd fall asleep and quickly this became enough comforting for him to go down for a nap. I tried to do this at night, but with limited patience usually gave in and nursed. Then one night, he decided he was over it...and never nursed again!
After that night we used the rocking to get him to sleep. And by 'rocking' I mean, held sideways and vigorously swung from side to side! lol Not that gentle rocking!
My son is 20 months old now and we still work on the best way to get him to sleep. It's always a work in progress with good days and bad days. Two steps forward and one step back. He's in his own toddler bed though, and depending on my level of patience, have no struggle or tears at bed time, though it takes a while of game playing/power struggle...he goes down with hugs and kisses and some nights sleeps all the way through...but always ends up in our bed first thing in the morning, which is fine with us.
I just think it takes a bit for the kids to readjust to routine and to switch one thing for another. Also, I think they catch on after a couple days that something has changed permanently and freak out! I.e., the first couple days of not rocking him to sleep went fine...and then he realized that wasn't a fluke, I really wasn't rocking him, and he panicked. It takes a lot of patience and understanding that some days are going to be good, some days are going to be bad and to not get attached to either outcome too much! Eventually, EVENTUALLY, they'll put themselves to bed and sleep through the night all on their own. And like nursing, which I was SO through with...we'll miss the days they needed us so intently :(
(i totally cried when he'd weaned himself! i didn't KNOW that last night would be the last! if i'd known, i wouldn't have gotten so frustrated that it was taking him so long to fall asleep... i would have treasured it for what it was...the end :( )