There are many versions of this, as he said it many times to different groups over the years, but I think this might be my favorite one, it was written by Martin Niemöller a survivor of the Dachau Concentration Camp.
First they came for the Jews
and I did not speak up - because I was not a Jew.
Then they came for the communists
and I did not speak up - because I was not a communist.
Then they came for the trade unionists
and I did not speak up - because I was not a trade unionist
Then they came for the writers
and I did not speak up - because I was not a writer.
Then they came for the artists
and I did not speak up - because I was not an artist.
Then they came for the students
and I did not speak up - because I was not a student.
Then they came for the reporters
and I did not speak up - because I was not a journalist.
Then they came for me -
and by then there was no one left to speak up for me.
-Martin Niemöller 1955
http://www.youtube.com/watch?v=O3DI6iQlom8 "Normal" short version, but good
http://www.youtube.com/watch?v=ZcridvxfLBo&feature=related Really long version, and excellent if you remove the libtardness they put in near the end.
It was written not just about the Nazi's, but also as a condemnation of anyone who would sit idly by while others committed great evil, or injustice.
Another quote to keep in mind:
All that is required for evil to flourish is for good men to do nothing
-Sir Edmund Burke
Don't forget the strategy of the left is to try to divide us, and come at us one group at a time, we must learn from history, and not let that happen, we have to be united, and we have to fight them wherever, and whenever they strike no matter how small of a thing they do, we cannot yield an inch.
We shall go on to the end, we shall fight in France,
we shall fight on the seas and oceans,
we shall fight with growing confidence and growing strength in the air, we shall defend our Island, whatever the cost may be,
we shall fight on the beaches,
we shall fight on the landing grounds,
we shall fight in the fields and in the streets,
we shall fight in the hills;
we shall never surrender
-Winston Churchill, June 4th 1940
ETA: Should we forget any of this I fear we may find ourselves in a new situation:
.....whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness. Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes; and accordingly all experience hath shewn, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the forms to which they are accustomed. But when a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, it is their right, it is their duty, to throw off such Government, and to provide new Guards for their future security.
-Declaration Of Independence