Here are a couple great resources for beginning couponers.
Queen Bee Coupons has a database that lists the prices at Costco for over 400 items. She has each item broken down into unit price and also lists the Amazon price for several items. I have been working on my own list like this of the items my family buys, but in the mean time I refer to this one all the time.
This Beautiful Frugal Life recently posted her stock up price spreadsheet. This is extremely helpful for a new couponer. There are many items that I haven't figured out the best price for so I appreciate having this list as a reference point. I also really like her disclaimer that her stock up price may not be your stock up price. You have to decide based on your family and your budget how much you are willing to pay for a particular product.
Thanks to these two bloggers for taking the time to put together such great resources.