Cornell University's Cooperative Extension (Ithaca, NY) has a great gardening section. There's so much information there that you'll feel overwhelmed! Most of the information is general, not region-specific, so there's something for just about every gardener.
There's a Home Gardening website, the Department of Horticulture's Gardening Portal, gardening factsheets, and even distance learning classes, including an upcoming class on organic gardening. But perhaps the most valuable section is the publications store, whose navigation is unfortunately somewhat hidden. But it has a ton of printed resources that you can buy–written by CU scientists and priced very reasonably. I have one of their many publications on composting.
So if you're in the market to buy gardening resources, I recommend checking with Cornell first before you hit the bookstore. You won't find slick, glossy books here but you will find sound, science-based gardening information.