Here is just a sample for you.
Chael Sonnen
Nate Marquardt
Alistair Overeem
Rousimar Palhares
Lavar Johnson
Brian Bowles
Big Ben Rothwell
Antonio "Bigfoot" Silva
Vitor Belfort
Robert Drysdale
Gilbert Melendez
Anderson Silva
Jon Jones
Josh Barnett
Tim Sylvia
Stephan Bonnar
Kit Cope
Royce Gracie
Phil Baroni
Sean Sherk
Hermes Franca
Dennis Hallman
Edwin Dewees
Chris Leben
Ken Shamrock
James Irvin
Thiago Silva
Christiane "Cyborg" Santos
Muhammad "King Mo" Lawal
Rafael Calvalcante
Joey Beltran
Thiago Tavares
Kevin Casey
Brian Ortega
Piotr Hallman
Hector Lombard
Gleison Tibau
Josh Burkman
This doesn't include the instances such as Dennis Siver who was taking post cycle steroid to restore his testicles, Randleman submitted a sample that didn't even contain human hormones, Wand ran from sample takers in 2014, Cro Cop admitted to using HGH, Randy Couture admitted to using HGH, Jeff Monson admitted to using steroids, and pretty much all the top guys in Pride were juiced to the gills. I can also amend the list and start giving you Bellator guys.