I've yet to go through all 10 pages though I will, some of what I've seen some of the posts mention Fusion players rather than Prog, unless the intent was "progressive" vs. Prog as in Prog Rock, bassists.
While after Prog I got deep into Fusion, as it was the time for that genere, and still have a lot of time for guys like Percy, Mark Egan, Jimmy Haslip, Scott Ambush, Jeff Andrews (RIP), Jaco, Stanley, Ralphe, etc. etc. they're not Prog Rock players like the usual Squire, Lee, Rutherford, Greg Lake, etc. I would suggest a similar thread for Fusion players, there are so many great ones. But...I'll always be a hardcore Prog person.
Bands like The Dixe Dregs / The Dregs fall a bit outside pure Prog to me but are certainly very progressive. I'm not even sure how to categorize Tull, the Glenn Cornick, who I love, days were one thing and the post-Cornick days were something else.
As I believe this to be this is a Prog Rock thread and as the masters Squire, Schulman and the like have already been mentioned, I'd add some that might not be here, like Jon Camp/Renaissance, Joe Macre & Carey Ziegler/Crack The Sky, Werner Frangenberg/Triumvirat, Gary Strater/Starcastle, Carl Cadden-James/Shadow Gallery, John Siegler/Utopia, Lee Jackson/The Nice, and a ton of others who aren't coming to mind at the moment.
And if talking Neo-Prog then there are Dave Meros/Spock's Beard, Pete Trewas/Marillion/Kino/Transatlantic, Jonas Reingold/The Flower Kings, Thomas Miller/Symphony X, and a ton of others who aren't coming to mind at the moment.
(if you don't know this, you will thank me for it, is arguably up there with Close To The Edge or The Gates Of Delirium or Supper's Ready, the end, with the Taurus pedals, is right out of Supper's Ready)
For kinda Prog/New Wave there was Sandy Horn of The Spoons....
And then there were these guys, who were just brilliant, check East To West