I just started doing livestrong.com. I'm tracking my weight (by graph), my exercise and calories. You can just track what you want, but this is why I chose this site:
1) every food that I pulled up to track was already in their database
2) I can search gazillions of recipes then save the recipe in my box AFTER I tweak it for SBD AND it will figure out it's new nutrition for me.
3) I can enter my personal recipes and have it list nutritional information.
4) It's free
5) I like Lance Armstrong and his foundation
Seriously, I had never counted calories before and had found it quite daunting. This is so easy for me and it gives me calculation each day as to how many calories I can eat and still lose 2# per week taking into consideration how much and what type of exercise I do that day.
I'm mighty happy with my weightloss so far, and I'm joyous that I've maintained this weight for over a year but....I'm ready to lose some more.
I know you only want to track weight but I couldn't help but mention the other benefits 'cause I'm pretty excited right now.