You may already be familiar with the concept of a sale cycle. It essentially means that there is a week or two out of each quarter for the store that an item is going to be at it's absolute lowest price. There are always exceptions to every rule, and in this case you may see highly competitive items like sodas and cereal hit this rock bottom price more than once a quarter.
If you use coupons this is a way to get great savings and sometimes free items. If you don't use coupons that is ok. This concept can be applied to non-grocery items and also relates to frugal living tip #7. Sales cycles are not only based on quarterly sales in the store, they are also based on seasonal demands. Think about it, fresh produce is always at it's lowest price during the months that it is harvested.
I wrote this post back in November 2010 that breaks down what months things tend to go on sale. I hope it helps you.
Feel free to ask any questions.