Go to your pharmacy and pick up the red "$50 in Great Savings" booklet and use the $2 coupon that's in there (it expires on 6/30/09). This turns out to around 7-9c per diaper - the retail price on most diapers is 25 or 26c).
Last time Walgreens had a deal like this, I ordered a special shipment from my local Walgreens manager in order to take full advantage of this offer. For the coupon, the register will usually take $2 off each pack, but it depends on your store's register (I've been to the same store and one day it will take $2 off each pack and the next day it will limit it to one pack per transaction). Remember that since the $2 coupon is a Walgreens coupon rather than a manufacturer's coupon, you can keep it and re-use it. In my opinion, the Walgreens premium diapers (the ones in the green pack) are of similar quality to the high end brands.
Remember - if they don't have the size you want, get a raincheck so you can go back at any time in the next few months to get the same deal.
And... if you took advantage of the Huggies deal I wrote about last week, this is a great way to use up your $10 register receipts that you received.