I found the entire Colbert performance at the White House Correspondent's Dinner (in an unusual bit of posting, Crooks and Liars only posted half of it, and the video is of poor quality):
Colbert: Part I
Colbert: Part II
Also, someone at Kos posted a complete transcript. It's funnier live, but some of the jokes come across more clearly in print.
THANK STEPHEN COLBERT HERE!
White House Correspondents Dinner