Some of these are harder and more abrasive than others:

King Crimson (really depends from album to album!)
Tool
Mastodon
Peter Gabriel’s first few solo albums.
Peter Gabriel-era Genesis
1970s-era Yes
Pink Floyd
Under the Sun
Enchant
The Mars Volta
Emerson, Lake and Palmer (avoid anything after “Brain Salad Surgery”!)
Spock’s Beard
Jethro Tull

Jimi Henrix Experience—“Electric Ladyland” (has some prog roots)
KISS—“(Music From) The Elder”—their lone stab at prog-rock, a horrible commercial failure, but one of their best albums despite sopunding completely unKISSlike
Black Sabbath—“Volume 4”, “Sabbath, Bloody Sabbath” and “Sabotage” were very proggy and very good. Rick Wakeman of Yes guesting on keyboards.
Led Zeppelin—“Houses of the Holy” and “Physical Graffiti” albums were classic, and also rather prog-influenced.
Queen—“Queen II” was by far the most prog-rockish of all Queen albums.

And there are many, many others . . .