Originally Posted by
Digifiend
Quite a few have three or more. Other than the already mentioned Carol, Monica, and Clint, there's...
Amadeus Cho: Mastermind Excello, Prince of Power, Totally Awesome Hulk, Brawn
Rachel Grey/Summers: Phoenix, Marvel Girl, Prestige
Jim Rhodes: Iron Man, War Machine, Iron Patriot
Alex Power: Gee, Zero-G, Powerpax, Powerhouse
Julia Carpenter: Spider-Woman, Arachne, Madame Web
Noh-Varr: Marvel Boy, Protector, Captain Marvel
James Buchanan Barnes: Bucky, Winter Soldier, Captain America
Steve Rogers: Captain America, Nomad, The Captain
John Walker: Super-Patriot, Captain America, U.S.Agent
Of course quite a few others have had two:
Franklin Richards: Tattletale, Powerhouse
Jean Grey: Marvel Girl, Phoenix
Cassie Lang: Stature, Stinger
Susan Storm-Richards: Invisible Girl, Invisible Woman
Betsy Braddock: Psylocke, Captain Britain
Sam Wilson: Falcon, Captain America
Jane Foster: Thor, Valkyrie
Gwen Stacy: Spider-Woman, Ghost-Spider
Toni Ho: Rescue, Iron Patriot
Pepper Potts: Rescue, Iron Woman
Oh, looks like I was ninja'd on a few of these.