ugh, i would not recommend the atkins "diet" for a bf mama.. atkins involves putting your body into a state of ketosis, which IMO is not a good idea for a nursing mama.. actually not a good idea for any person who wants to lose weight and maintain a lower weight and be healthy at the same time.
weight watchers IS a smart choice for people who aren't already super knowledagable about calories, starches, sugars, and how to eat smart.
here are some tips:
avoid refined sugars and starches w/ no nutritional content (most pastas, rices and breads that aren't whole grain)..
fill up on lean meats like chicken, turkey, fish, and seafood (not fried, though)..
eat lots of veggies, steamed or roasted..
yogurt and cottage cheese are good.. oatmeal is good...fruits are good, fresh is best.
remember that anything you buy fresh (rather than canned or processed) is always going to be better for you..
good luck, mama!