Shorpy is a photo blog that specializes in posting old pictures (no personal affiliations here), and one delicious aspect of it is that there is a great selection of scans from 4x5 Kodachromes.
Yep, Shorpy is a great photoblog. They have a lot of nice B&W work, too. Including some cool ephemeral subject matter you don't see presented online very often.
I've also seen some of those same Kodachromes in the online collections hosted by the Library of Congress and the National Archives.