Would you believe I just recently discovered Tarkus? Great stuff. I have a soft spot for 70's era prog-rock, so I always love to find new good examples. Personally I think PF's Animals is an underated album, and has some of Gilmour's most inventive guitar work, but I can understand how it doesn't really have wide appeal. Btw one of my all-time fave bands is Yes. Don't know if you've checked them out much but I'm still blown away by their live album Yessongs even though I've heard it countless times. They have an expansive almost mystical sound which at times is reminiscent with what's on Dark Side of the Moon.
I remember a good friend introducing me to ELP with Tarkus way back in my fast-times-at-some-high-school days. Yes, Rush, Robin Trower, oh man, good listening times in college. Then, in my senior year at college, added arena bands, like Boston and Kansas, and stumbled into Fleetwood Mac and Heart. Absolutely loved the first two Boston albums, with Schultz's misfit genius talent and Brad Delp's voice. Just a great sound to my ears.
R.I.P., Mr. Delp. Like many other talents, you left us way too, soon. Your voice lives on.