I’m a fan of all sorts of music, and that includes most styles of metal, old and new. It is fairly universal to acknowledge bands like Led Zeppelin and (especially) Black Sabbath as some of the progenitors of what we now call “heavy metal.” What’s occasionally overlooked is some of the roots of metal in Psychedelic rock.
A lot of psychedelic rock may not be what you would ever consider “metal” — yet at the same time there are definite trends in late 60’s psychedelic music that foreshadow what we would now categorize in that genre. Even so, while Jefferson Airplane’s “Somebody to love” was pretty extreme music at the time, I don’t think anyone would call it metal. Likewise with Pink Floyd’s early music, particularly songs like “Astronomy Domine” — while it was a lot heavier than most music coming out at that time, is not really what we’d call metal (though if you’ve heard the Voivod version of that song, you may beg to differ).
There were a lot of isolated songs like the ones aforementioned, but probably the most metal-like that I can think of, which pre-date the metal genre, would be the Beatles’ Helter Skelter, Pink Floyd’s The Nile Song, and possibly even the Who’s Boris the Spider.
A lot of folks might say that the Beatles were not a psychedelic rock band. I don’t want to get into a long consideration of what exactly would qualify one to be a “psychedelic” rock band, but I think it’s safe to say that at the time Helter Skelter was released, they were as much a psychedelic band as they were anything else. Helter Skelter is a thrashing mess of chords and near screaming vocals that is probably the most well known song that is as close to “metal” as most anything that pre-dates metal as an established genre.
Unless you are fan of pre-Dark Side of the Moon Pink Floyd, you have probably never heard The Nile Song. It is from Pink Floyd’s first and only (unless you count “The Wall”) soundtrack album, known as “The Soundtrack to the film More” or simply, “More”. Wikipedia has a short clip of the song in ogg format that gives an idea of how heavy — uncharacteristically so for Pink Floyd, generally — that song really is. Wikipedia also points out that it is one of the few Pink Floyd songs which does not feature any keyboards.
The Who weren’t really “psychedelic” and Boris the Spider isn’t really “metal” — but it is pretty plodding and creepy/gloomy sounding, and features one of the first examples (that I can think of) of a deep growl used for some of the lyrics, almost prescient of the style of singing later used in early death and thrash metal. Also, I just really like the Who and wanted an excuse to add them to the list. I used to maintain that I can see for miles was also a proto-metal song, but I think I’d lose that argument with most people.
Of course, these were all isolated instances of extremely heavy songs by bands which otherwise played a variety of styles of music. It wasn’t until you found bands which stuck almost exclusively to a very heavy style (eg, Black Sabbath) that metal as a genre could probably be said to have started. Still, it’s hard to hear these pre-metal songs and not see the close parallels.

I’m a fan of multiple music types too, although I do have a leaning towards more rock / metal, which in the past has often been too quickly dismissed (or denounced) by Christians. Makes me sad :(
Still - mostly listening to http://www.christianrock.net these days (some good stuff, some not-so-good) and really liking Skillet.