One of my favorite websites is a blog at http://babycheapskate.blogspot.com/. It's a great resource for all things baby and toddler on sale. Something I have been using already, in preparation for our little bitty witte, is a cheat sheet for good diaper deals. I've shown it above (click on the image to see it enlarged) and you can find it here:
It lists quantities per diaper size and the price to beat, so that you know you're getting a good deal.