Sweet Peas, Lathyrus odoratus, have always been one of my favorites. We grew the cultivated types a few times when I was little, but they were never very reliable in our climate with such hot and humid summers. I've not had much luck with then since then either. If you look at English gardening books or nursery catalogs, you will find tons of sweet peas so I can only assume that the climate there is more to their liking. The exception is our native wild Sweet Pea which is pictured. The colors can vary slightly, but this is pretty typical, though you will occasionally see the odd white one. They grow across the road in full sun, happily coexisting with weeds and other wildflowers. The kind of ramble over other plants and can spread for quite a distance. They are impossible to transplant - at least I don't know of anyone who has had success - but this fall, assuming I can collect some seeds before the critters get them, I'm going to try to start some from seed so I can have some on this side of the road where I can enjoy them without walking down the road. They bloom from mid-summer until frost here and don't seem to be bothered by either insects or critters that eat plants. As a plus, they are nitrogen fixers, so a few in the garden would be a plus for more than their beauty.
Please note that although garden peas (Pisum) are quite edible and delicious, Sweet Peas (Lathyrus) are poisonous, both the flowers and the peas.
For a quite detailed history of the Sweet Peas, see http://www.ngb.org/gardening/fact_sheets/fact_details.cfm?factID=17
I've been working on wild flower photos, so there will be some more in the days to come.