I'm using the term somewhat losely to describe a living mathematician or very abstract theoretical physicist.
Modern Mathematicians Everyone Should Know

John Guckenheimer
Philip Holmes
Steven Strogatz
Perelman - the guy who proved the Poincare conjecture

I looked him up immediately. I am not really familiar with Canadian mathematicians, shame on me. He sounds a little interesting. I haven't seen any of his books (no surprise there). I take it that you like his work?

These are what I could think of to add:
10) William Thurston
11) John Milnor
12) Walter Rudin (Wrote the gold standard Analysis texts)
13) Grigori Perelman for sure!!
14) Richard Hamilton
15) Marston Morse (Died 1977)
16) Bertrand Russel (Died 1970)
17) Michael Spivak (another amazing author- hands down one of my favorites)
18) P. R. Halmos (Died 2006)
19) Ian Stewart (Publishes many mainstream books as well as texts)
20) Steven Krantz (A prolific author of both mainstream and textbooks)
21) Jerrod Marsden
I have tried to read Marsden & McCracken's The Hopf Bifurcation and Its Applications .. NAAASTY!! (It was for a project)
And also I have a book called:
Manifolds, Tensor Analysis, and Applications
Let me just state that the very first thing you come across is the Axiom of Choice =) And it ends up with apllication of tensor analysis to high-energy plasma physics..

Hahaha, that's a good one. The Emperor's New Mind is also a real roller coaster. It starts with talking about the philosophy of mathematics and recurring digits in pi, and then ends up talking about areas in the brain were quantum effects can take place and neurons.

you really could have just written "So personally, I would view Einstein as a Physicists who's research has contributed greatly to Mathematics." rather than that rediculously long thing.
My appologies, sometimes I like to get philosophical.

These are what I could think of to add:
10) William Thurston
11) John Milnor
12) Walter Rudin (Wrote the gold standard Analysis texts)
13) Grigori Perelman for sure!!
14) Richard Hamilton
15) Marston Morse (Died 1977)
16) Bertrand Russel (Died 1970)
17) Michael Spivak (another amazing author- hands down one of my favorites)
18) P. R. Halmos (Died 2006)
19) Ian Stewart (Publishes many mainstream books as well as texts)
20) Steven Krantz (A prolific author of both mainstream and textbooks)
21) Jerrod Marsden
I have tried to read Marsden & McCracken's The Hopf Bifurcation and Its Applications .. NAAASTY!! (It was for a project)
And also I have a book called:
Manifolds, Tensor Analysis, and Applications
Let me just state that the very first thing you come across is the Axiom of Choice =) And it ends up with apllication of tensor analysis to high-energy plasma physics..
oooooohhhh! That book has a juicy title!
God, the Axiom of Choice is a pain in the mathematical rear that will never go away in our lifetime. I wish that we as a Mathematical Community could just make up our minds and either accept it or reject it!

@ColdCoffee:
Most modern mathematicians have accepted it.. Though it entails some interesting implications, such as the Banach-Tarski paradox.. =) ..

you really could have just written "So personally, I would view Einstein as a Physicists who's research has contributed greatly to Mathematics." rather than that rediculously long thing.
That may be so, but I, for one, being somewhat uneducated relatively speaking, appreciate the content of the post.
That is why I posted it, I assume that many people on this forum are not Ph.D. holding mathematicians or Graduate Students in math, a lot of people do not understand the distinction between Math and Physics. Personally, I was a Physics major before I switched to Math. At the time I thought they were practically the same major so to me switching was a minor thing. By my Junior year, I saw the difference very clearly.

@ColdCoffee:
Most modern mathematicians have accepted it.. Though it entails some interesting implications, such as the Banach-Tarski paradox.. =) ..
Almost every one that I know has. I only know one professor here that (at least closetly) rejects it. He is actually the one that got me into Topology. Every once in a while, walking down the faculty office halways you heard discussions about the axiom. Its fun.
Whats your background, if you don't mind my asking?

@ColdCoffee:
Most modern mathematicians have accepted it.. Though it entails some interesting implications, such as the Banach-Tarski paradox.. =) ..
Almost every one that I know has. I only know one professor here that (at least closetly) rejects it. He is actually the one that got me into Topology. Every once in a while, walking down the faculty office halways you heard discussions about the axiom. Its fun.
Whats your background, if you don't mind my asking?
I don't. I am a graduate student in mathematics and physics. I am finishing my thesis on mathematical modeling of type 1 diabetes at the moment.
My university aims at giving one a well-rounded mathematical upbringing, so I have had courses on differential geometry, foundations of mathematics, concrete and algebraic structures, statistics and propability calculation, analysis (of course), linear algebra, topology and mathematical modeling.
I noticed that you are a graduate student in mathematics - did your university apply the same approach?
I would like a definition of "modern mathematician," before I get into this thread..