The two I have seen most people use are fitday.com or sparkpeople.com. I use the NutritionData website a lot to look at specific foods, but they also have a tracking and blogging mechanism within their "MyND" dropdown menu bar. You can find the main site at http://nutritiondata.self.com/
Just be aware that your macronutrient ratios (proteins, carbs, fats) for SB will likely not match up very well with "standard" recommendations, especially in P1. Dr. Agatston simply doesn't follow these or gear his menus or dietary recommendations to these kinds of specific "targets".