I'm working on a research project about vampires, and I'm trying to incorporate a variety of sources. Obviously I can't just skip Dark Shadows, but there are like a billion episodes. I would really appreciate it if anyone could tell me some of the most important episodes of the show, and/or any episodes that deal with crosses and other holy objects. Thanks! :-)

You're correct. There are at least a billion episodes.

I remember watching Dark Shadows as a kid. But, I don't really remember a lot of specifics.

Concerning information on the episodes, you might like to check out the information that you find on the following site.

Dark Shadows - Episode Guide