Best players ever to have played in the MLS (not necessarily only players that did their best there, or who are considered to be the greatest MLS players of all-time, but considering their ability at their peak; there are a couple of MLS greats though, who didn't always do particularly well elsewhere however)

To be finished:
-Kléberson
-Carlos Ruiz
-Eddie Pope
-Donovan Ricketts
-Cobi Jones
-Jaime Moreno
-Marco Etcheverry
-Raul Diaz Arce
-Brian McBride?
-Claudio Reyna
-Chad Marshall
-Ozzie Alonso
-Tony Meola
-Predrag Radosavljevic (Preki)
-Taylor Twellman
-Jeff Agoos
-Nick Rimando
-Mauricio Cienfuegos
-Jay Heaps
-Chris Henderson
-Chris Klein
-C.J. Brown
-Piotr Nowak
-Marcelo Balboa
-Jason Kreis
-Steve Ralston
-Jeff Cunningham
-Kevin Hartman
-Jimmy Conrad
-Pablo Mastroeni
-Carlos Llamosa
-Guillermo Barros Schelotto
-Luciano Emilio
-Alex Pineda Chacón
-Andre Blake
-Mike Magee
-Miguel Almiron
-Robin Fraser
-Omar González
-Brad Davis
-Brian Ching
-Ben Olsen
-Taylor Twellman
-Christian Benteke

Honourable mentions:
-Pelé, Beckenbauer, Chinaglia, Banks, Cruyff, Eusébio, Best, Bettega, and Morini, etc. who played in the NASL, which was a precursor (it's because of that that they aren't starting)

-Paolo Barison