For an online reference, I like the Missouri Botanical Garden's "Plant Finder" at http://www.missouribotanicalgarden.org/plantfinder/plantfindersearch.aspx

Or you can type in the common or botanical name of the plant and "missouri botanical garden"

With the MO Bot plantfinder website you can either type in the plant's name or you can type in your requirements and it will spit out a bunch of suggestions. Really great resource that I use a lot.

If you add a general location to your zone 8, it may help since zone 8 WA is different than Z8 GA or Z8 TX. Depending on which you are in, you may find some of the links below useful.

The Chicago Botanical Garden has some sets of plant trials on line, though not a comprehensive database.

Another resource for is the Ladybird Johnson Center's plant finder, though I use that rarely since it doesn't have as much overlap with my growing conditions.

UConn has a woody plant database.

Dave's Garden has a plant database, but it tends to sometimes have inaccuracies IME, so use it with some skepticism, and check other resources.

For woody plants, Michael Dirr has an app based on his book The Manual of Woody Landscape Plants. I use it and like it.