The line is actually "ich bin ein Berliner." There's an urban legend that what he actually said was "I am a jelly donut" but that's disputed.
It's one of the most famous speeches of the Cold War era and probably Kennedy's most famous (then again my personal favorite was his "We shall go to the moon" speech but that's just me being a geek).
Everything you ever wanted to know about that line is here: http://en.wikipedia.org/wiki/Ich_bin_ein_Berliner
I searched it and found out that "Ich bin ein Berliner" happens to be "the one and only correct way of expressing in German what the President intended to say."
I think this is a very famous speech. Even Australians know this
line. When it comes to things American Presidents have said,
I think "ich nin ein Berliner", "it's the economy, stupid" (Bill Clinton)
and "yes, we can" (Barrack Obama) are lines that people all over
the world know.
I actually have a book of the speeches of Barrack Obama....never
thought I'd buy something like that.....but it's interesting, some of
the things JFK said (e.g. Ask not what your country can do for
you, ask what you can do for your country) really inspire and
make you want to be a better person. I get the same feeling
from Barrack Obama.