I assume, based upon your list, that you are asking for standup comedians, rather than groups of comedians.
In no particular order:
Bill Cosby (mostly for his standup work, although some of his TV work was good too.)
Bob Newhart (Again, mostly for his standup work, but again, his TV work was good too.)
Jerry Seinfeld (This time mostly for this TV work, but his standup was good too!)
If you were allowing comedy groups, my list would have:
The Marx Brothers
Monty Python Flying Circussssss
The Three Stooges
My three cents worth
In no particular order:
Bill Cosby (mostly for his standup work, although some of his TV work was good too.)
Bob Newhart (Again, mostly for his standup work, but again, his TV work was good too.)
Jerry Seinfeld (This time mostly for this TV work, but his standup was good too!)
If you were allowing comedy groups, my list would have:
The Marx Brothers
Monty Python Flying Circussssss
The Three Stooges
My three cents worth