Steve Hill sent out a link for Perennial Resource sponsored by Walters Gardens. It reminded me of one of my favorite resources Heritage Gardens. Steve also mentioned the local wholesaler Kerbo Nursery that has some great photos of Oklahoma hardy's.
Coming from the Northwest, Heritage Perennials at http://www.perennials.com/ was one of my favorite sources for unusual but available perennials. As a salesman I couldn't wait for the "Blue Pot" truck to show up. Their quality was consistently exceptional. However, now that I'm so far away from the maritime clime of the western seaboard, I can visit by Internet. Heritage Perennials has a great website resource, updates, newsletters, handy tables, calculators and even ask an expert. You can search by plant characteristics, such as color, height, soil, butterfly or bird attractor.
It is easy to become overwhelmed by the number of resources available, but every now and then I run across these outstanding sites that really are interested in getting you hooked on perennials. Perennial gardening is like a drug. After they get you started on the reliable performers, you will be back for the more needy, rare and exotic. Soon your aesthetic values will change, and the more common but reliable Geranium x cantabrigiense 'Biokovo' will leave your affections as your most favorite perennial. It will be replaced by the more subtle beauty of the Hellebore and the Heuchera.