Following is a list of possibilities, most of which come from Water Conserving Plants for the Pacific Northwest West of the Cascades (by the N.W. Perennial Alliance, 1993). The list includes only trees that 1) thrive in soils which are waterlogged in the winter, and, 2) grow to less than 40 feet tall.

ACER (maple):
A. buergeranum (trident maple)
A. campestre (field maple)
A. ginnala (Amur maple)
A. circinatum (vine maple)

CORNUS nuttallii (western dogwood):

CRATAEGUS (hawthorn):
C. douglasii (black hawthorn)
C. monogyna
C. phaenopyrum (Washington thorn)
C. x lavallei (Carriere hawthorn)

HOVENIA dulcis (Japanese raisin tree)

MALUS fusica (Pacific crab apple)

NYSSA sylvatica (black gum)

OXYDENDRUM arboreum (sourwood)

PRUNUS (prune/plum/cherry):
P. virginiana var. melanocarpa (chokecherry)
P. emarginata (bitter cherry)

PYRUS (pear):
P. communis (common pear)
P. pyrifolia (Chinese pear, sand pear)

QUERCUS (oak):
Q. acutissima (sawtooth oak)
Q. imbricaria (shingle oak)

RHAMNUS purshiana (cascara)

Season Winter
Date 2006-05-23
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I think that your best bet may be a maple. Three maple species surfaced that meet your criteria of a quick growing, 20-30 feet tall tree with an equal or greater spread, that will do well in the sun.

--Acer circinatum, the vine maple (the only downside--this may be a bit shrubby for your landscape)
--Acer ginnala, the Amur maple
--Acer palmatum, the Japanese maple (you'll need to be choosy in order to find a cultivar that will reach 20-30 feet, but there are some that do. Additionally, A. palmatum will tolerate drier soils than A. circinatum.)

Sources:
The Pacific Northwest Gardener's Book of Lists , R. & J. McNeilan, 1997, p. 18, 27, 30.
Tree & Shrub Gardening for Washington and Oregon , A. Beck & M. Binetti, 2001, p. 244-249.
Trees & Shrubs for Northwest Gardens , J. A. Grant & C. L. Grant, 1990, p. 56-58.

Season All Season
Date 2006-05-23
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I found an interesting page from UC Davis. They appear to have had success rooting cuttings of A. triflorum:
http://rooting.ucdavis.edu/rec00001/r0000468.htm

I also found information from a UK source about germinating the seeds of both Acer species. The abbreviations under Tree Seed Pre-treatment will help you determine the required conditions (in the chart):
http://www.nickys-nursery.co.uk/seeds/pages/bonsai-info.htm

Season All Season
Date 2008-01-10
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Root weevils are the most common pest attacking Rhododendrons in the Pacific Northwest so they can only be temporarily eliminated from any garden. If the environment is right and their food source returns, so will the root weevils.

If you want to keep your current Rhododendrons, the weevils can be controlled if you’re diligent (forever!?). However, it sounds as if you’re willing to remove them and start fresh. Some of the most susceptible (host plants) are Rhododendron and Azalea, Heather, Salal, Manzanita and Kinnikinnick, Pieris, Maples, Viburnum, most Conifers, Astilbe, Cyclamen, Helleborus, Hosta and Primrose.
(Source: Root Weevils in the Nursery and Landscape; Identification and Control, by J. DeAngelis and G. Garth, EC 1485, Oregon State University Extension Service).
http://extension.oregonstate.edu/catalog/pdf/ec/ec1485.pdf

The following website has an excellent list of resistant Rhododendron varieties: http://cru.cahe.wsu.edu/CEPublications/eb0970e/eb0970e.pdf.

Season All Season
Date 2008-01-24
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I am sorry to hear about your diseased maple. Your rare species was mentioned in 2 of our 3 books on maples. However, none of the books describe pests or diseases species by species. The books only give information on "general maple problems." The Gardener's Guide to Growing Maples by James Harris states that maples are "generally trouble-free," but the following can cause problems:
Verticillium wilt, which can kill a tree in a few days, or branch by branch over many years; it is a soil borne fungus that is quite common in Seattle (sorry);
Fusarium, which is another soil borne fungus;
Botrytis, which is a fungus, worst on seedlings, but can also cause die-back on established plants; this fungus favors warm humid conditions;
Die-back, which is not a disease; new growth in fall is not hardened off by winter-time and is killed by cold temperatures.

Take a sample branch into a Master Gardener clinic for a diagnosis (insist they submit it to the CUH diagnosticians if they do not know).

If it is Verticillium you can only slow down the disease by reducing all stress on the tree (keep it well watered and mulched). If your other maples are healthy and established they should be okay, but all are vulnerable to this nasty fungus.

Season All Season
Date 2006-10-10
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There is information about Verticillium wilt and how to manage it on the Washington State University Extension's website

To have a sample from your Japanese maple diagnosed, you may want to contact WSU Puyallup Research and Extension Center at: www.puyallup.wsu.edu
go to "How to Submit a Sample," scroll down to "Plant Problem Diagnosis," then you can download a form by clicking on "Form C1006."

My personal experience with this disease is that the Japanese maple lived with it for quite a few years before totally succumbing, at which point we had it removed by an arborist.

Season All Season
Date 2006-10-23
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Here are some of the plants which are available in September: Achillea (Yarrow)
Alstroemeria (Peruvian lily)
Aster
Callicarpa bodinieri (beautyberry)
Cotoneaster (for foliage)
Dahlia
Echinops
Elaeagnus (foliage)
Eryngium
Heather
Hebe (flowers and foliage)
Helichrysum (straw flower)
Lavender
Acer (Maple: foliage)
Quercus (Oak: foliage)
Skimmia
Limonium (Statice)
Viburnum tinus

Here is a link to the Washington Park Arboretum web page of seasonal highlights.

Season All Season
Date 2007-03-03
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