is now not a good time to mention that my DD was 5 before this happened... 5 I tell you!!!! It wasn't until a good friend of ours had a baby who she could put in the cot awake, walk away and the baby would gargle for a bit and then fall asleep without any fuss.. My friend told my DD that her baby could go to bed on his own, so DD should be able to...
That very night DD decided that I could kiss her goodnight and I could leave her... We never looked back, oh until the next night when DD decided that it wasn't a good idea and she wished she had never agreed to it...
We didn't ever give in again, normal bedtime routine, book, cuddle and kiss, then we layed with her for 2 mins (and only ever 2 mins) and then left.. We had to go back every 15 mins or so, just to see her until she was asleep but it was a start...
Even now at 12 yr old she still asks for the 2 mins.. which occasionally I do, as I find if she asks it usually means she has something on her mind she wants to chat about....
Hope you crack it. don't wait as long as we did until you get tough ;-)