Some nice features of the site: you can log meals. For instance, I usually eat Kashi Autumn Wheat cereal for breakfast. I always have my bowl with flax seeds sprinkled on and I use whole milk (one of the by-products of having an 19 month old child. I refuse to buy two kinds of milk.) I have this set as my "Kashi breakfast" so I can input all three items at once. You can also input a recipe, so you can figure out the nutrition of something you make often.
If you're really enthusiastic, you can log your exercise in too. You can even set a weight-loss goal and it will tell you how many calories you need for the day (subtracting the ones you burn from your goal). There are "dares" you can take such as eating less sugar or talking a daily multivitamin. You can join groups with similar goals as you. There are plenty of articles and blogs to read as well. All this, and it's free. I'm sure there are some fancy features if you are willing to pay, but I am not.
I've heard that there are other sites that have similar types of things. Sparkpeople is the only one I know off the top of my head. I'd already been using Livestrong when I heard of Sparkpeople, so I decided to keep using it. I've been an on-off user for a couple years now. If you want to become friends with me on Livestrong, my user name is kestie77.