Get Out of Town! - my Dad's book and web site on the natural areas of Indiana. Check it out, order a copy, and get going!
Indiana Native Plant & Wildflower Society is a great place to check for activities and information. They also have an annual native plant auction & sale - definitely worth checking out!
Oklahoma Wildflowers - this page has excellent photography, and a huge variety of plants. Definitely one of the better wildflower pages out there.