Enter the portion control diet. This is the only diet that I've been successful with, and I've been doing it for just over a year now. The reason I'm able to sustain it, is because I can eat whatever I want. For example, I eat ice cream every night if I want, but only a scoop, and when I go out to eat, I split my entree and take half home. The only caveat is that I try my best not to eat processed food; if I can't make it at home with whole ingredients, then I will likely not eat it.
I can now look at a plate of food an know exactly how much will fill me up (this took a while). So, even when I don't leave the table feeling full, I know I'll feel satisfied within 15 minutes. I used to love the feeling of being overstuffed, but now I just feel sick when I overeat, and I don't enjoy it.
I've lost over 30 lbs in the past year using the portion control method. It's not a lot, but it's a healthy reduction, and one that I know I can sustain.
I know everyone is different when it comes to dieting, both mentally and physically, but I just wanted to share my experience with the most successful diet I've ever undertaken. I hope someone else can benefit from my anecdote.