Low fat or diet processed foods.  
It can be hard to lose weight using low fat diets. Although low fat processed foods have been popular for more than 15 years, cases of obesity are rising as each year passes. This is due to lots of low fat diet foods having large amounts of hidden sugars, (be wary of any ingredients ending in 'ose', ie. sucrose, dextrose, fructose, they are all forms of sugar!) Eating processed foods that claim to be low fat is not always the answer to losing weight.

Low calorie/no carb diets plans.
You won't lose weight using a low calorie dieting plan either. In fact, restricting your calorie intake could be the worst thing that you can do to your body, since that will only slow down your metabolic rate, (the body's fat burning engine), and ruin all chances of losing weight (low calorie diets may allow a few pounds of weight loss for the first few days, much of it water and lean tissue, notably muscle. After that all weight loss could come to a halt).
Low/no carb diets have recently become popular over the last couple years, but the problem with low/no carb menus are that they can be too restrictive and hard to follow for most people. It is never a good idea to cut out a whole food group from your diet. Low carb diets menus tend to rob your body of too much energy, (carbohydrates), and make it nearly impossible to remain on the program for very long.

Healthy, balanced whole food eating plan and regular exercise.
It might not be as trendy as the latest diet fad in the glossies, but it works!

Your body needs the right type of fats, the ones it can't produce, called EFA's, (Essential Fatty Acids), mainly Omega 3. (Look for oily fish, walnuts, eggs, leafy green veg, etc.)

Your body also needs enough calories in your diet, from a balanced spread of food groups, (dairy products; meat, fish, nuts and pulses; fresh fruit and vegetables; bread, cereals and grains.) Aim for a rainbow of colours in your fruit and veg section.

It also needs the correct type of carbohydrate for your energy needs, especially if exercising. (Look at whole meal, brown or unrefined bread, pulses and foods with a low glycaemic index; i.e. foods that release their sugars slowly over a longer timescale.) Try to eat organic rather commercially farmed foods.
 

Things to avoid; deep fried foods, crisps, biscuits, processed foods, and any food that has ingredients you can't pronounce or don't what they are! 

Things to cut back on; alcohol, caffeine, red meats, salt, and saturated fats.