It is backwards to be thinking about what plants you need to obtain before thinking of how the design will be laid out and what it will accomplish. The spaces that are available and the functions that need to occur will guide the plant selection. Most everyone has plants they like and try to find a place for, but you must find the place where it makes sense to use that particular plant. You can't skip the design process and expect to end up with "something different [better]." Builders invest nearly nothing in the design process. They hire someone who doesn't understand it well to come up with something barely passable (because the public doesn't understand it either) and then repeat this formula ad infinitum. It's like halfway designing once for thousands of homes. [Obviously, to those who have seen my suggestions here, I'm not against the use of a formula. But it must be a good formula and be applied correctly and specifically to the architecture and site conditions ... what builders never do.]

The resource that would help you is a landscape designer, as you probably don't have time to work through the process from scratch.

Agree -- either hire a landscape designer, or don't plant right away, and take some time to observe the site and develop your own ideas of what you are going to use it for, traffic flow, drainage, and other needs. Or both.

This may mean that you miss the fall planting season . . . but there's always spring.

Also, local county extension agents and master gardener programs are extremely helpful, if available in your area.

For an easy overview of the unfamiliar garden plants you're seeing, you might go to the local public library and look for books about garden plants for your region. And if you're looking for a particular book your library doesn't own, their Interlibrary Loan service can obtain it for you (sometimes charging a small fee).
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"Plants for a Livable Delaware" talks about invasive plants which should be avoided, and those which might be substituted for particular invasives.
http://www.dnlaonline.org/information/plants_for_delaware.php
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The University of Delaware Botanic Garden has -- besides the garden itself -- plant info, events, plant sales, etc.:
http://ag.udel.edu/udbg/
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NCSU has wonderful lists of garden plants in various categories (bulbs to trees, and everything in between). I've seen this information in the same format for other states, so I assume there's a USDA database which the states adapted for their particular climates. Unfortunately I could not locate such a database for Delaware (though that doesn't mean there isn't one). Anyway, NC's zones include DE's zones, so the NC database would be useful for you:
http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/index.html

First, click on the category you're interested in. Then choose whichever arrangement of data presentation is most useful. Don't ignore the "By Scientific Name" and "By Common Name" at the top of each category.

Thanks everyone. I didn't mean that I'd just start to plop in the plants. After 30 years of doing this, I know better! ;) I'm going to take measurements draw a basic plan next week when we are there.

missingtheobvious, I really appreciate the links because I just didn't know where to begin. I guess that a trip to the library while we are there would also be good, to look at books of the local gardens (which I'm pretty sure they have).

Our builder has chosen the plantings and designs for his previous homes. They're not bad, but all very similar (and he uses a lot of spirea which I like, since we have 87 of them on our current property, but not for the new house...).

I'll do some preliminary planing, and get a design started next week. It's difficult, being in a new location, but we don't have enough in our budget for a professional to do this. Perhaps I could find a nursery nearby that could help? It's worth a try...

Is any of the house built? If so take a few pictures while you are there.

If you get a chance this season (before November), try to stop in at Mt. Cuba Center for some ideas; it's just northwest of Wilmington, DE. They focus on plants native to our region and have some lovely display gardens as well as a large trial garden. Lots of information, too, on their web site ... check out the Native Plant Finder under 'Gardening Resources', where you can browse their entire list of native plants.

You could also check for any other public gardens in your area; they should give you some good ideas about what works in the area and various plant combinations.

I'm in coastal NJ, about midway up the coastline, a very similar growing environment, and I think you'll find you have a lot of options - narrowing it down is going to be the tough part. Have fun!

Here is a link that might be useful: Mt. Cuba Center

"I didn't mean that I'd just start to plop in the plants." If the question, then, is more like, "What are some nice plants one might consider using in a zone 6a DE landscape?" you might also consider asking it in the New England, Shrubs, Trees or Perennials forums.

Or even the Mid-Atlantic Gardening forum.

Mid-Atlantic is going to be a more appropriate forum than New England.