One of my favourite topics for reading is the history of physics, and the 
development of the A bomb at Los Alamos and the scientists involved.
The two people I like reading about most are Richard Feynman and John
von Neumann, two great minds but very different personalities. My
question is, the two must have met each other, but has one ever
commented on the other in an accesible printed source, or is there any
third party comment anywhere on what one thought of the other.

Richard Feynman spoke highly of John von Neumann, who was both a
mentor and a friend. Feynman mentions von Neumann several times in the
book "Surely You're Joking, Mr. Feynman!".

From page 79 of "Surely You're Joking, Mr. Feynman!: Adventures of a
Curious Character" (ISBN 0393316041):

"Johnny von Neumann was the greatest mathematician around."

From page 132 of the same book:

"Then there was John von Neumann, the great mathematician. We used to
go for walks on Sunday. We'd walk in the canyons, often with [Hans]
Bethe and Bob Bacher. It was a great pleasure. And von Neumann gave me
an interesting idea: that you don't have to be responsible for the
world that you're in. So I have developed a powerful sense of social
irresponsibility as a result of von Neumann's advice. It's made me a
very happy man ever since. But it was von Neumann who put the seed in
that grew into my active irresponsibility!"

From page 172:

"Finally there came in the mail an invitation from the Institute for
Advanced Study: Einstein... von Neumann... all those great minds! They
write to me, and invite me to be a professor there!"

I cannot recommend this book highly enough. It is a witty, wise,
wacky, and entirely delightful account of some of the adventures of
one of the most remarkable men of our times.

Amazon: "Surely You're Joking, Mr. Feynman!": Adventures of a Curious Character 
http://www.amazon.com/exec/obidos/tg/detail/-/0393316041

Feynman also praises von Neumann in "The Pleasure of Finding Things
Out: The Best Short Works of Richard P. Feynman." On page 229, Feyman
refers to von Neumann as "the world's greatest mathematician." This
book reprints the story cited above in which Feynman tells of the
advice he received during Sunday walks with von Neumann.
 
Amazon: The Pleasure of Finding Things Out: The Best Short Works of
Richard P. Feynman
http://www.amazon.com/exec/obidos/tg/detail/-/0738203491

John von Neumann is said to have appreciated Feynman for both his
intellect and his sense of humor:

From page 102 of "John Von Neumann: The Scientific Genius Who
Pioneered the Modern Computer, Game Theory, Nuclear Deterrence, and
Much More," by Norman MacRae (ISBN 082182676X):

"Johnny [von Neumann] apparently intimated to contemporaries that he
found a relaxing sense of humor mainly in Fermi and the young Richard
Feynman, although also among more personal friends such as Ulam.
'But,'" said one Nobel Prize winner, 'from people like Leo Szilard, or
Robert Oppenheimer, or even Albert Einstein, he tended to distance
himself (this is my impression)'."

From page 137 of the same book:

"Nobody even now should pretend that the last word has been said on
quantum mechanics. A modern system of visualizing them came later from
the American physicist Feynman, whom Johnny [von Neumann] regarded as
tremendous fun."

Amazon: John Von Neumann: The Scientific Genius Who Pioneered the
Modern Computer, Game Theory, Nuclear Deterrence, and Much More
http://www.amazon.com/exec/obidos/tg/detail/-/082182676X

I hope this is precisely the kind of information you seek. If anything
is unclear or incomplete, please request clarification; I'll gladly
offer further assistance before you rate my answer.

Very best regards,
pinkfreud

Just the answer I wanted, so quick as well. Plenty of references for
me to look up and study further.
Thank very much pinkfreud-ga