Have you given up beef because you don't think it fits with your healthy eating habits? I think beef has gotten a bad rap. My hubby is a red meat and potatoes man and I have learned to make us both happy.
There are lots of leans cuts of meat:
The list goes on.
If you want specifics look under the Core Plan in your Eat Wisely book to see what Weight Watchers considers lean beef. Look here to find the leanest cuts of beef.
A serving size is 4oz cooked and is about the size of a deck of cards. It really is enough to satisfy most appetites.