Diann, Sieboldii is indeed a pretty performer and does well in Z6 or warmer, but unfortunately, it's not an evergreen.
There is one evergreen, Trish, that I didn't think about before. If you want one that isn't going to eat the house, you might want to consider cirrhosa 'Freckles'. It's a really fun clematis with an interesting coloration and bloom. Here's a link:
http://simplyclems.com/data/im.... 'Freckles' is an Evison cultivar, hardy in Z6-11, is quite mannerly, and tops out at 10 feet max.
EDIT: Link should not have period at the end. Correct link is:
http://simplyclems.com/data/im...
=)
