Macy's Pride would be perfect. It's gets about 5 ft & blooms almost non-stop. It's very hardy & has great disease resistance. it's not pure white though. In cooler weather, its has a yellow tone to it.

You might want to consider Sally Holmes. 5 to 8 ft.

This is the biggest white rose I grow. Darlow's Enigma.

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Now you won't have room for anything else....

Rosa Rugosa Alba--very hardy, fragrant, blooms almost constantly, gets lovely autumn foliage and enormous red hips. It does sucker and will fill up your space. It gets get 5-6' high. It doesn't want to be sprayed and except for cleaning out dead wood, never needs to be pruned. It's also very thorny. Deer and rabbits leave it alone, as do dogs, stray children and burglars.

Frau Karl Druschki
Paloma Blanca
Martine Guillot

Roses Unlimited should have these.

Old Baylor, a Pioneer rose from Antique Rose Emporium, and Linnea's Rose from Rogue Valley Roses.

Thank you so much for all the suggestions! I am so excited I have been reading up on all the varieties suggested. I think I may actually be buying a couple of the varieties listed above, I particularly love the look of Frau Karl Druschki, and Macy's Pride, but I can't find where to buy the macy's online? But feel free to keep on with the suggestions, I'm thinking of adding a few roses to the other side of my garden as well :) they are quickly becoming as addictive as my hydrangeas LOL LOL

The Rose Man Nursery carries a good selection of Easy Elegance. Their website is www.therosemannursery.com.

What about Blanc Double de Coubert?

Here is a link that might be useful: Blanc Double de Coubert

If you are looking for a white rose that resembles a florist rose, Frau Karl Drushki may be the only such rose that is hardy enough to make a robust shrub in your climate. However, like most roses, it will get black spot in the East unless protected with fungicide. (Spray Bayer Disease Control every two weeks.)

For a no-spray large landscape rose, Darlow's Enigma is probably the best choice, but the flowers are very small.

Another possibility would be the Hybrid Musks Penelope and Kathleen. These make large clusters of medium-sized flowers. They are more disease resistant than FKD but may have cane loss in subzero winters, if those still occur in your area.

These will all thirve in zone 6. As for disease tolerance, consult others in your more immediate area.

Morden Snowbeauty
Winchester Cathedral
Claire Austin
Blanc Double de Coubert
Ilse Krohn Superior (Climber, can be pruned as a large shrub)
White Grootendorst
Darlow's Enigma
Sally Holmes (will dieback, but vigorous enough to easily reach 5ft+ each year)
Trier (climber/rambler that will dieback, but vigorous enough to easily reach 5ft+ each year)

I second catsrose. As long as you don't mind a rose that suckers, Rosa Rugosa 'Alba' is a great rose. That's it's only trait that you may or may not want. They are sometimes used for a hedge.

A white rose, really white, that is very hardy, get's no disease and blooms very profusely up and down the canes-is Karl Forster. It's a hybrid spinosissima thus blooms somewhat earlier than most roses, mine is already leafed out. It makes a big arching bush with light green, small leaves. Flowers are a sort of muddled many petaled form with good fragrance. The bush is covered with flowers. Available from Pickering and others which is a good sign for a rose introduced in 1930.

Here's a link to a picture of Rosa Rugosa 'Rubra' used as a hedge: http://www.landsteward.org/page.cfm/10356