Here is a link to an article by Stuart Rothenberg listing open House seats and vulnerable house seats. I don't kinow if it is too late to run candidates in these districts, but it is worth a look:
http://www.realclearpolitics.com/articles/2008/04/dangerous_dozen_open_house_sea.html
http://www.realclearpolitics.com/articles/2008/04/dangerous_dozen_open_house_sea.html