Most people seem to be using one of the following resources to help keep track of calories. These sites have a big database of foods and also provide other useful features such as recipes, weight tracking etc.
http://myfitnesspal.comThis is the most well known but I hear that it nags you about not eating enough on fast days.
http://www.fatsecret.co.ukThis has lots of uk supermarket foods already in its database. It does not nag you about not eating your recommended daily allowance on fast days.
Both these sites have free apps for your smart phone making calorie counting almost pain free!