I use a combination of Blue Book, forums, and other websites. I have found that while Blue Book is usually fairly accurate, occasionally it can be WAY off of what actual market value is. Forums usually have one or members that are big C&R guys that are a great resource for determining value. I've also reached out to sites like oldguns.net that specialize in collector stuff and the admins were very helpful.
Like T.L., I'd be happy to share whatever knowledge I have based on the guns you have. Good Luck!