I have had a hard time IDing some of my Geraniums until I found a page that shows them all. Now I know Exactly what I have.
Here is a link that might be useful: ID page
This website has pictures of a large number of individual geranium flowers. I found it interesting and also valuable in identifying geraniums. Click on the geranium pages. It also contains pics of other flowers as well, on different pages.
Here is a link that might be useful: geranium flower pictures
Here is another website with many hardy geranium pictures and descriptions.
Here is a link that might be useful: Hardy Geranium pictures