Plants for a garden arch

Lathyrus odoratus varieties are the ones that only last a season - the everlasting sweet pea is called Lathyrus grandiflorus, and there is also Lathyrus latifolius. You could grow ivy if you want to, but it does tend to take over everything - make sure you choose a variety of Hedera helix rather than any of the others. There is a plant called Trachleospermum jasminoides which is evergreen and has fragrant flowers which would do well in the situation you describe, but as you're in the States, I don't know how cold you get in the winter there, so you'd need to check whether it will survive your winters. Google it and see;-)