You missed probably the most important (IMO) 70s progrock band - Genesis.
Start with Selling England by the Pound, since its their most solid release from beginning to end. From there go with The Lamb Lies Down on Broadway (their concept album and most mature offering, musically, from the Peter Gabriel era) and Foxtrot (some really key songs from their catalog on this one, including their 20+ minute epic Supper's Ready). If you really dig Foxtrot, check out Nursery Cryme and Trespass last, cause those two are the hardest for new fans to get into, even though Nursery Cryme has two of the best songs they've ever written (The Musical Box and Fountain of Salmacis), much of the album is *very* subdued. The live album is cool if only for the version of The Knife thats on it, since it blows away the studio version on Trespass.
I don't acknowledge Genesis past The Lamb Lies Down on Broadway, so someone else is gonna have to step in to give Collins-era reccomendations
As far as King Crimson goes, theres less to breakdown, I'll just give you the essentials from each era:
late 60's - 70's
** In the Court of the Crimson King
** Larks Tongues in Aspic
** Red
(note that ItCotCK has a *very* different sound than the latter two albums, due to a totally different lineup, and Crimson's knack for constantly evolving (read:
progressing ) their sound, however since its the first KC album, and arguably the album that created progressive rock, it is essential.
1980s:
** Discipline
** Three of a Perfect Pair
1990-2000s:
** THRAK
** The Power to Believe
With Rush, you're golden starting with anything from 2112 through Moving Pictures, with Moving Pictures being the most logical choice for most newbies. I *highly* reccomend going with A Farewell to Kings or Permanent Waves from there. 2112 loses some steam after the title track (which is worth the price of the album alone) and Hemispheres is amazing, although I just personally dig AFtK and PW more.
Like most of the other 70s progrock bands (King Crimson being the one huge exception) Rush forwent their roots for a more mainstream sound in the 80s, although out of all of them Rush is the only one that maintained some amount of integrity (going for a mainstream ROCK sound as opposed to mainstream POP - like Genesis and Yes).