Yes - I could have added Greenslade, also Henry Cow (though perhaps an acquired taste, like Gong!). I could also have mentioned Rush, but they don't float my boat. I detest ELP which is why I didn't mention them - I'd call them 'keyboard metal' rather than prog, especially as they do a lot of classical 'interpretation'; The Nice were better IMO, especially their version of West Side Story's 'America'.
These days you have Porcupine Tree, Dream Theatre, Steve Wilson, Goldfrapp, Sid Arthur, Mercury Rev, Flaming Lips, Big Big Train, The Besnard Lakes, and many others .. and there have been plenty of other progressive artists over the years, such as Björk, Kate Bush, again too many to mention.