All current iPad prices and availability can be seen in our live iPad Price Guide (an abridge version also posted below). Apple has the best prices on the iPad 4 with Retina display by a few bucks, while MacMall is offering the best price on the 16GB iPad 2 at $329 ($70 off) and the entirety of the iPad 3 line while supplies last.
It's also worth nothing that while Apple won't ship new iPad mini orders for two weeks, MacMall tells us it has virtually the entire product line in stock, including cellular models. (The only exception being the 16GB white and black WiFi models, both of which ship to customers next week, which still beats Apple by a week. ) Wal-Mart and Target also have a handful of minis left for online shipping.
And don't forget to sell your old iPads for cash to the varioustrade in services). It helps offset the cost of the new model, in some cases by hundreds of dollars.