The one that seems the most popular overall is MyFitnessPal. I read an article the other day that 68% of people who use counters use that one. It seems to have a pretty broad existing food database too.
I am using one called FatSecret. I'm planning to move to MyFitnessPal at some time soon.
I had a few questions on MyFitnessPal and posted here a couple days ago. A few people mentioned what they liked and what they didn't. Hope this will be helpful!
http://www.3fatchicks.com/forum/gene...al-please.html