I discovered that trying to organize this list of characters is next to impossible, mainly because I only wanted each person/demon/vampire/dead person on ONE list. Having tried this, and not being satisfied, I'm just going to put people on the lists that they qualify for, this still being somewhat subjective. But hey, I can do that.
I'd also like to clarify my classifications a bit. Major supporting characters are characters that have appeared in three or more episodes, unless I feel a special dispensation is warranted. So, a person who has been on twice, but made a lasting impression on the show will be labeled a major supporting character. There are a few people who have been on three or more times, but whom I do not feel qualify for major supporting, Devon being one that comes to mind. I feel like Linneaus. Oh, the power!
Major Supporting Characters
Minor Supporting Characters