Better late than never....
1) The Nice - one of the predecessors of Emerson, Lake & Palmer. Some of ELP's live shows have material sourced from Emerson's old group
2) Emerson, Lake and Palmer - unsurpassed and as overblown as Emerson & Lake's egos. Bigger than life music and definitive prog rock. My all time top group......
3) Triumvirat - German group that had a real ELP sound about them
4) Yes - renowned for the long (and I do mean long) tracks. IMHO Wakeman did better here than by himself
5) Genesis - both before and after Peter Gabriel. Complex works - The Lamb Lies Down on Broadway is one of the better prog rock examples
One area close to this style of music came from one Larry Fast recording as "Synergy". This was totally electronic (from the mid-70's) and was ground breaking in terms of synthesiser playing (he backed Peter Gabriel, Kate Bush et al as well as producung his own work). Utterly spectacular work, considering the analog synthesisers & technology used.
h9k