I have always struggled with menu planning. I have developed many complex ways to plan out my menus, from once a week to planning a whole month at a time. Nothing has ever worked well for me. Each week's menu and list making took me around an hour, sometimes more. It was ridiculous.
Then I stumbled upon The Happy Housewife, right when she was introducing her Menu Planning 101. I linked to part 4, which has links to the previous 3 "lessons".
If you have trouble with your menu planning, I highly suggest that you give this a try. It has really, really worked for me! I now sit down, look over the sales, quickly pick out my menu for the week, and write my grocery list based on that. I am on my 3rd week, and I'm loving it! It is saving me so much time!