Check out this site
Free Calorie Counter, Diet & Exercise Journal | MyFitnessPal.com
Really great - you enter your details and each day enter the foods you've eaten - they will either be in the list or you can add to it.
Enter your exercise - includes horse riding too - tells you the calories/carbs/fats/proteins you've eaten for the day and relates it to the exercise you've taken.
Loving it - you can produce reports too that graph how you're doing.