Rumble Johnson. Don't hear a lot about him lately because he's in WSOF but I think he's become a monster and would smash most lhw's if they let him back in the UFC
OnlyTheStrongSurvive -KevinMcAllister - Rich FranklinThis.
This is largely due to undercutting Anderson's resume.
I think there should be a distinction between under-rated and under-known by more recent fans.
A good case of under-rated would be Bisping imo. He's not the best, he's failed over and over to break the cream of the crop but most would think he's B level (sub-top 10 or something). He is just under elite level (like top 5 or cream of crop). He does not suck.
BJ Penn is pretty under-rated now days. Same with Matt Hughes. Same with Fedor. Basically anyone that was good before that isnt now wasnt ever shit to chunks of todays fans.
Din Thomas. Got unlucky a few times. Beat several guys mentioned on this page. 
Its hard to disagree with Frank Edgar! The guy brings it, and really has never been clearly beaten in the UFC. All his fights have been super close.
Phillip Miller & Rulon Gardner both retired undefeated... Just sayin..
Click this thread with expectations of I got on first page
Wasa-B - BJ Penn is pretty under-rated now days. Same with Matt Hughes. Same with Fedor. Basically anyone that was good before that isnt now wasnt ever shit to chunks of todays fans.
This 100%.
OnlyTheStrongSurvive -Guys been top 5 in my book since he stopped being #1 in his division almost 10 years ago.. Mans a legendKevinMcAllister - Rich FranklinThis.
Pro Ice -Voted up great post
There are a lot of fighters that get love and recognition here but are relatively unknown to newer fans like Vovchanchyn, Pele, Ruas, Bustamante, Sakurai, Sato, Uno, Zinoviev
Like many have mentioned Mezger's very underrated great stand up decent ground. fought some of the very best and was a threat to beat everyone of them
So many underatted / under appreciated, here's a few others that I think really deserve mention
Tyoshi Kohsaka = One of the best resume's ever (Fedor, Couture, Rutten, F Shamrock list goes on) - great grappler - was in almost every fight
Masakatsu Funaki = JMMA pioneer - did more for the sport than most realise - great ground subbmission game - how good he could've done in prime really a ?
Kiyoshi Tamura = Great grappling - First to defeat a Gracie (Gracie's accepted) - drew prime F Shamrock
Mitsuhiro Kanehara = One of the best fighters with a losing record - - great grappler - some very legit wins in his prime - tremendous heart - left everything in the ring
Kazuo Takahashi = Great resume - could hang with the very best - always came for war
Mamoru Yamaguchi = Pioneer first ever shooto 125 & 135 champion - very well rounded could ko or submit
Daisuke Nakamura = Incredible ground skills - 15 + armlock/bars subs 3 flying = most in mma competition i believe
Kazuo Misaki = Been mentioned - great resume - could hang with the best - always comes to FIGHT
Allan Goes = Great ground skills - intense - arguably beat 3 of the GOAT
'Macaco' Jorge Patino = Vale Tudo legend - won a title 18 yrs into career - came to fight
Johill de Oliveira = V/T, Luta Livre legend - 1st to beat Pele - won 4-5 v/t tournaments - only 3 losses (Wallid, Pele) before accident in Pride and eye injury
Vitor Ribeirio 'Shaolin' - Shooto champion - one of the best 155ers for years - incredible ground game
Marcus Aurelio = 21-10 w 18 finishes - one of the best 155ers at one point- half loses are arguable - never finshed in 30 + fights
Alexander Nogueira 'Pequeno' = Great resume - arguably the best 140lb in the world for years - arguably the best guillotine ever in 'mma'
Volk Han = Incredible grappling - proved he could hang with the best in mma at 40 yrs old
Mikhail Avetisyan = Russian mma pioneer - won 1st 32 man tourny - one of the best leg lockers ever
Amar Suloev = Great striking great throws - could hang with the very best
Mikhail Illoukhine = Great grappler - won 4-5 no rules tournaments
Dave Menne = UFC champion - great resume - could hang with the best - always came to fight - tremendous heart
Carlos Newton = Mentioned - UFC champion - great ground game - fought and beat some of the very best in his prime
Ronald Juhn - Stephan Palling - Ray Cooper - Falinko Vitale are some Hawaiians that deserve mention these guys all fought some of the best in the world and where all threats to beat anyone of them in their prime - all warriors
Didn't mean to go overboard, guys just keep coming to mind
Ok two of the lesser known MMA fighters that don't get enough love - Martijn de Jong and Sergy Bytchkov
Thanks Kobayashi
Bytchkov definitely deserves mention the guy was a BEAST and one of the most excitig
Here's a Bytchkov thread I made if anybody wants to check
http://www.mixedmartialarts.com/mma.cfm?go=forum_framed.posts&thread=2120796
Jake shields