This list is reproduced from the Atkins (UK) website document "low carb foodlist" (PDF download link), with some adjustments to language and presentation while retaining the lists themselves.
The core of your food intake should be protein sources with ample inherent fat. Typically 4 to 6 ozs of meat/fish/poultry would be a portion size for protein in a meal. That's 115 - 175 grams of food, giving you 20 to 35 grams of actul protein content. The smaller weight is appropriate for women while the largest value is appropriate for men of average or above average height. Tall muscular men engaging in strenuous activity may merit an increase to 225 grams of meat etc per meal but Atkins is not a "maximum protein" diet. An alternative guideline is a piece of meat or fish about the size of the palm of your hand.