I've used FitDay in the past - it's pretty great. You can log your food as well as your exercise and your fitness goals, and it has some pretty cool reporting functionality. Based on how you log your food and exercise, it will report on calories in vs out, as well as how close you are to meeting your daily nutritional goals (e.g., it alerted me that I need more calcium in my diet). There's a free version on the web, or you can download a deluxe version for a fee - I've only used the free version, and it does a great job.