And I'm not talking about tournament winners so there's no reason to bring up the likes of Steve Jennum.
It's gotta be Dave Menne.
He won the middleweight title in a lackluster fight in disappointing event and then lost it badly in his first defense. Unfortunately, what he's most remembered for is later getting crushed by Phil Baroni.
Honorable mention goes to Sean Sherk. When's the last time anyone heard that name? I think Barao and De Randamie will definitely be added to the list soon enough.
There are the obvious ones like Menne who were champions outside the modern era after winning somewhat arbitrary title fights (Menne fought for the title immediate after being KO'd in Rings). Then there are the legit champions who have been forgotten...
Tim Sylvia was a real beast. He got a lot of shit for his style and his overall goofiness but he had great boxing, good kicks, legit TDD and serious KO power. He was picking Big Nog apart before being submitted and put a textbook boxing clinic on Brandon Vera back when Vera was a badass.
I wouldn't say Rich Franklin has been forgotten but I don't think he is talked about in the same way that he should be. If we put everyone in the context of their era he is an all-time great. When people think of MW champions they just think Silva, it's almost like anything before him didnt exist. Rich was a DOMINANT fighter before running into Anderson.
Frank Shamrock defended his LHW title multiple times. He's not really in a lot of discussions anymore either.