dooooommmm!!!
Pentagram were one of the bands that invented the stoner/doom metal scene in the early 70's. sadly, they never really achieved the commercial success of bands like Black Sabbath but that hasn't stopped them from making some of the best music in the genre. their greatest hits album, First Daze Here, at the very least, should be in any self-respecting classic rock fan's collection. Be Forewarned is one of my favorites from them.
Place of Skulls is sort of a doom super group. Victor Griffin from Pentagram founded it and it also features Wino from The Obsessed and Saint Vitus among others. musically, it's an obvious progression; a little heavier than Pentagram and more modern sounding, but still the same sludgy riffs underneath. the only catch is that Griffin converted to christianity a few years back and the lyrics have been reflecting that more and more. With Vision is the title track off their most recent album.
check these out if you like any of: Black Sabbath, Blue Cheer, Kyuss, Queens of the Stone Age, Mastodon, Trouble, Saint Vitus, or the Obsessed.