Black Sabbath… it would be wrong to create an album that falls under the stoner rock label without referencing Black Sabbath. Ask any band in the scene and Sabbath will be one of their influences. In terms of transitions and changing time signatures, they were brilliant. My favourite example is in Iron Man at 3:40 – it goes from the one riff to the next so smoothly and I have listened to that particular transition so many times.
Another classic from Sabbath in which the transitions are great, as well as the dynamics.