RowFast- Although my weight loss hasn't been as huge as some of the people on here, my weight loss goals were pretty much the same as yours and I have been able to maintain it for the first time in my life.
How? Well, this is where it gets tricky... and your right, it's the hardest part. People don't like to hear this, but truthfully, it is a lifestyle change. I kept experimenting until I found substitutes for the "bad" foods I was eating, cut back on my carbs and increased my fruits and veggies. Almost every "bad" food has a tastier substitute if you just experiment a little. To be honest, I like my "new" foods better.
So basically, to maintain, you continue with your healthy choices, just add more healthy snacks and increase your portions slightly to get into a maintenance calorie range instead of a weight loss calorie range. Same foods, bigger portions basically. The minute you go back to "just one" of this and a "taste" of that you gain it back.
I can't speak for everyone, but this is what has worked for me.
Reached 30 lb. Weight Loss Goal April, 2010
Fighting The Battle to Maintain
When something goes wrong in your life, simply yell "PLOT TWIST!" and move on!