If you're willing to go with a refurb, you can get the first generation iPad directly from Apple at a discount of up to 24%: 16GB Wi-Fi & 3G for $399.
In order for the 3G part to work, you have to pay just like a cellphone for monthly service, but if you have a home network, Wi-Fi works just fine, plus you can use it anywhere else that has Wi-Fi (McDonalds, Starbucks, etc.).
They dropped the price of the 16GB Wi-Fi only to $299 but they're out of stock at Apple store.
It's really hard to find iPads on discount. Apple is pretty protective of its products' retail values.
Another place to try is MacConnection (1-800-986-4420). You have to call to check availability.