I had about 150 deindexed domains from some very aggressive SEO testing 15-18 months ago. Over 75% of them have been reindexed between the last 2 Panda updates.
So you don't nessarily need to throw them. I just removed the majority of the internal OBL's and stopped backlinking to them for a year. Then I started some gradual article building links again, and hey presto...
Don't know if this will work every time, but I was amazed to get so many back, and some of them were GREAT URL's which is why I hung onto them to test the possibility (I gave them 2 years max to come back.)