I suggest using myfitnesspal.com as well as it is free. It helps you to monitor your caloric intake and be honest. It also helps you to think..."do I really need to eat that?". I use myfitnesspal and find it helpful. One caveat...when you enter your exercise there I think it calculates too high...so be careful "eating back" the exercise calories.
Since you are going to exercise...you will need to provide fuel. Try to eat whole foods...whole grains that have not bbeen processed to death. Eat fruit and veggies too. Watch your fat intake. Again this is a huge benefit of myfitnesspal in that it helps you to see nutritional info.
Hydrate with water, cut out empty calories as much as possible and cut out soda pop even diet as much as you can.
I got a book thru bicycling magazine called "Ride Your Way Lean". I read thru it and it has useful info.