Grape vines?

Honeysuckle?

I'd suggest a combination of vines for longer flowering time. Roses, or honeysuckle, as extia mentioned would be nice for their fragrance, as one of the elements. Your local nursery will have the best ideas for vines that do well in your particular area. You might also consider a row of pots containing the same (evergreen?) material to replace the gate, and two pots w vertical planting on the opposite end to accentuate the entrance/ exit point.

Cool Contraption! I wish I had one! Great suggestions above!

Love a pergola! Honeysucke attracts hummingbirds. That would be beautiful!

Have a group setting of furniture if you want to sit under.

http://houzz.com/photos/36205

http://houzz.com/photos/631933

http://houzz.com/photos/1831776