From time to time I see posts from people asking about specific plants... some posts ask for help with identification, information, seed, etc.
The US government maintains an extremely useful (if somewhat scientific) web resource that every beek should keep in their bookmarks:http://plants.usda.gov/index.html
There are many pictures, identification guides, range maps, and scientific data here. You can search by common name or scientific name, and I like this site as "conclusive proof" of a plant ID.
So.. check it out. I spend too much time browsing this site some times, but it does come in handy!