A.L.
I have the same problem and, frankly, I need this advice as much as you do.
I have tried just about everything. I talked to him, yelled at him, left him letters, talked to his parents, talked to his girlfriend, etc....
I even just dropped Torri off at his house when I had to go to work, effectively forcing him to watch her. But I found out that he wasn't really watching her. Instead he would be playing video games the entire day or locking her in another room so that he could have sex in his. Eventually she had to be rushed to the emergency room because he had locked her (she was almost 3 at the time) in the bathroom and told her to "go potty" while he was having sex. She took a bite out of a 1000 Flushes bar and they didn't know if it was poisonous or not (luckily she was fine).
Now I've gotten to the point where I don't even try anymore. He seems to try to make my life as terrible as possible so we just don't talk. And seeing as he hasn't paid child support or even kept a job in over 2 years I guess he just isn't trying. It used to bother me a lot but now I don't care as much and I just wish that he would terminate his rights to her. He hasn't been around to see her in so long that Torri doesn't even seem to notice and every time we speak of her father she responds with, "Oh. You mean Robert?"