One thing I've noticed is that I sometimes respond TOO quickly when my DS makes noise... like, sometimes when he reaches the end of a sleep cycle, he cries out for just a second. I used to run in and pop my boob in his mouth ASAP, but in the last couple months (he is 14 mos), I have waited a second and peeked around the door to watch him... About 2/3 of the time, DS is back to sleep in a second.
Another strategy I try is pulling the nipple out of his mouth when he's asleep, and then firmly putting my hand on him if he starts to root around wanting the boob again. He will squirm for a second, but about half the time he settles back into a deep sleep without nursing again.
Granted, these are mostly things I do at naps. I think they would probably be helpful at night, too, but I am usually half asleep and so tired that I just give him a boob so I can go back to sleep.