Well, you could start at the beginning with bands like Black Sabbath, Blue Cheer, St. Vitus, Pentagram, and Trouble. That can kind of branch a couple directions. As far as stoner rock/metal; in the early-mid 90's I was listening to bands like Kyuss, Sleep, Fu Manchu, Nebula, Masters of Reality, Monster Magnet and even early Queens of the Stone Age. High on Fire is one of my favorite bands of all time and, though I don't really think of them as stoner or doom, they get lumped in with that often, with good reason I suppose.
Another road off of the Sabbath caravan, in the more doom-ey direction, leads to Candlemass, Cathedral, Electric Wizard, The Obsessed, My Dying Bride, and later the mighty YOB in the mid 90's. In the last decade many of those bands remain active, Sleep has a new release for instance. Also in the last 10 years there have been some pretty excellent acts in this vein, and also some that are just kind of related or share some commonality. Bands like Graveyard and Uncle Acid have become massive, but there is also Red Fang, Monolord, Elder, Windhand, Pallbearer, Khemmis, Spirit Adrift, etc. That should keep you busy for awhile and I am sure you'll stumble into many other that are excellent like Dead Meadow, Melvins, Weedeater, Bongripper, Witchcraft, Sunn0))), Paradise Lost, Earthless, Acid King, Goatsnake, etc. etc.
Edit: I know I missed some boys, my intent was not to give a best of list. Also, aware my timeline might be a little off, but I think the OP will get the point.