moonflower is an annual so cold would not be a factor but i like the fragrance.
you can also try some of the fragrant tobacco (nicotiana alata). it is a dieback perennial for me but might not tolerate zone 7 winters. the fragrance of the white flowers can be quite powerful on warm evenings.
rhododendron viscosum is a native azalea that blooms in early summer and has white flowers with a nice fragrance.

I've long been a fan of night-blooming jasmine (_Cestrum nocturnum_). You can over-winter it indoors or in a greenhouse like any other tropical plant. Not having a greenhouse, I have two night-blooming jasmines over-wintering in the bathroom--one sitting on the windowsill, the other next to the sink. In a few weeks, I plan to pot them into large containers to sit outdoors for several months and perfume the night air. If over-wintering night-blooming jasmine is not your cup of tea, you can order plants from such mail-order nurseries as Woodlanders in Aiken, SC, or Logee's in Connecticut. Both these nurseries have Websits enabling online ordering; however, Woodlanders ceases shipping in March. You should, however, be able to pick up orders in person at a later date.

The fragrance of night-blooming jasmine is one that no one should deprive him/herself of. It's an incredibly fine scent.

The first time I saw the ornamental grass Muhlenbergia capillaris 'White Cloud' at night under a half moon, my heart skipped a beat. It doesn't have a scent, but at night, in a light breeze, the white inflorescences are gorgeous. I haven't seen it suggested for moon gardens before.

The species is native to our area, and the 'White Cloud' cultivar originated in Florida. I have a few planted together and the effect is lovely in daytime and at night. The only drawback is that it in a very strong wind, a few of the thin leaves will bend, so a protected area might be the best place. It does well in my clay (amended with compost) and likes as much sun as you can give it.

That sounds absolutely lovely, Georgia Transplant. I also want to create a moon garden, Karma, so am gathering ideas. The moon, of course. For us it needs go on the car-park side of the house so we can enjoy it walking in at night--before we get in and turn on the lights, and the TV. All the fragrant osmanthuses for spring and autumn fragrance, even if the flowers are tiny. The same for every fragrant viburnum I can get hold of, spread throughout the garden since the path to the door's getting awfully crowded in my imagination. Fragrant fringe tree for bloom after the native dogwoods finish is already there, though. Ginger lily for late-summer flowers and fragrance. Small well-behaved variegated ivys to help outline paths. Gardenias! Moonflower and nicotiana, already mentioned, are right at the top of my list. My mind's blanking out, but there are so many must-haves, including now definitely M. 'White Cloud.' That's going to need a special spot...

Oh my gosh! So many good ideas! It's almost overwhelming! I never would have thought of the "White Cloud", but after remembering what it looked like growing in Florida it is a "must have". My only worry is that my back yard gets a lot of wind. I am planning on butting the moon garden up to the corner of a privacy fence, so maybe this will help with the wind situation. The moon was so bright last night that I wishe terribly I already had the garden in place. Thanks for the inspiration! Oh do you think that I would probably have to order a "Night Blooming Jasmine" online, since this is not the right zone for them??