Mugatu and his piano-key necktie.
But seriously, I think it might help to think of them in categories. What brands/designers/tailors contributed to certain schools of thought or looks? So American/Ivy look, Neapolitan look, English look, Couture/Fashion look etc. Additionally, there are retailers (could be called "brands") that were innovators in both what they carried and the aesthetic they drove into the market even if they were less-than-successful business models. It would also be worth looking at what is driven the Japanese's buying as catering to their tastes has definitely had a huge influence on the luxury goods industry.
Intentionally leaving out non tailored clothing type folks so as to focus scope.
Gant (Guaranteed to bleed, anyone?)
Hickey Freeman/HSM (HMX corp)
(include bootmakers here? Red Wing, Frye, even the likes of Lucchese etc? larger question of what menswear means here)
Anderson & Sheppard
Gieves & Hawkes
Turnbull & Asser
Gucci (Horsebit loafers anyone?)
Ferragamo (Italian? He's technically a hollywood guy)
Yves St Laurent
Tom Ford (including his Gucci work here)
Interesting stores/business model innovation or preservation:
Loro Piana (really taken the fabric marketing to the next level, made it about the fabric and less about the designer)
Ede & Ravenscroft (Who else still sells all the stiff collars, etc?)
an HK Tailor like WW Chan who really work that travelling tailor bit/fast bespoke in HK.
I'm sure I'm leaving out everything important but mainly I think breaking this up into categories, then sorting out the top 50 based on inclusion of these key spheres of influence is probably the easiest way to go about it.