PHP Headers los mas populares Mime Types para tener amano.

Atom

header('Content-type: application/atom+xml');

header('Content-type: application/atom+xml');

CSS

header('Content-type: text/css');

header('Content-type: text/css');

Javascript

header('Content-type: text/javascript');

header('Content-type: text/javascript');

JPEG Image

header('Content-type: image/jpeg');

header('Content-type: image/jpeg');

JSON

header('Content-type: application/json');

header('Content-type: application/json');

PDF

header('Content-type: application/pdf');

header('Content-type: application/pdf');

RSS

header('Content-Type: application/rss+xml; charset=ISO-8859-1');

header('Content-Type: application/rss+xml; charset=ISO-8859-1');

Text (Plain)

header('Content-type: text/plain');

header('Content-type: text/plain');

XML

header('Content-type: text/xml');