Any digital one in the $20 range will be perfectly adequate. I like one that does grams as well as ounces because that's what I generally think in terms of.
There are many calorie counting sites out there. I know Fitday will let you do EVERYTHING by weight--it seemed to me that The Daily Plate, while better in many ways, did not have a "weight" option for some things.
The most important thing to know about your food scale is the function of "zero" (or z/t or "tare") button. This returns the counter to zero, ignoring everything already on it. So you can put a bowl on it, push the button, and it says zero. Then you put your oatmeal in the bowl, record the weight, and push zero. Then you put your fruit in, record that weight, push zero, and then you can put your walnuts in and record that weight. So you don't have to mess around with any dirty measuring spoon and you don't have to do any weird math.