Who do you think was pre dominantly a specialist at certain submissions in MMA? I'll get it started and state the obvious with Palhares and his heel hooks. 
Paul Sass triangles.
Minotauro - anaconda choke
There's some chick that does arm bars.
Alpha Males and the Guillotine. 
Mike Easton has been known to pull off a move that makes everyone gag.
Pettis is a beast on the mat and is very technical with all submissions.
Cody McKenzie (duh)
Fedor belly-down armbar
JonesStoleDC'sOlympicRibbonAndWentLOCO -Too soon bro.
Chael Sonnen, Triangle choke...I hear it's NASTY!
Pequeño Nogueira- guillotine.
Marcin held for leg stuff at lw
Thalee letes has a sick arm triangle
Luke rockhold has a nasty Kimura Choke
Jacare - arm triangle
Shayna baszler - shwing (leg Nelson chicken wing)
Megumi Fujji - everything, especially toe hold
Hazelet - modified armbar/ omoplata
Übereem - guillotine
Rani yahya - north south choke
Milton vierria - different arm triangles
Palhares - heel hook
Rhonda - arm bar
Rickson - arm bar
Big nog - anaconda
Bj penn - rnc
Joe Stevenson - guillotine
Imanari and his leg locks.
Wifespowerbottom -He is Jordanesque in his ability to pull it off!!!Casual Kiwi - Luke rockhold has a nasty Kimura ChokeBest chokes are kimura chokes
Some Von Flue guy was good at something I think..
Bret Hart - Sharp Shooter
Dustin Hazelett with all kinds of weird submissions