In-lines CSS, JavaScript, and images.

inline.php

#!/usr/bin/env php
<?php

	define(SUCCESS, 0);
	define(ERROR,   1);

	if (count($argv) != 2) {
		printf("usage: %s <filename>\n", basename($argv[0]));
		exit(ERROR);
	}

	$filename = $argv[1];
	if (!file_exists($filename)) {
		printf("Please choose a file that exists.\n");
		exit(ERROR);
	}

	$dir = dirname($filename) ? dirname($filename) . DIRECTORY_SEPARATOR : "";

	$document = new DOMDocument("1.0", "UTF-8");
	$document->loadHTMLFile($filename);

	// CSS
	$links = $document->getElementsByTagName("link");
	$stylesheets = array();
	for ($i = 0; $i < $links->length; $i++) {
		$link = $links->item($i);
		if ($link->getAttribute("rel") == "stylesheet") {
			$stylesheets[$i] = $link;
		}
	}
	$css = "";
	foreach ($stylesheets as $stylesheet) {
		$css .= file_get_contents($dir . $stylesheet->getAttribute("href"));
		$stylesheet->parentNode->removeChild($stylesheet);
	}
	if ($css) {
		$style = $document->createElement("style", $css);
		$head = $document->getElementsByTagName("head")->item(0);
		$head->appendChild($style);
	}

	// JavaScript
	$scripts = $document->getElementsByTagName("script");
	foreach ($scripts as $script) {
		$src = $script->getAttribute("src");
		if (!filter_var($src, FILTER_VALIDATE_URL)) {
			$src = $dir . $src;
		}
		$script->removeAttribute("src");
		$script->appendChild($document->createTextNode(file_get_contents($src)));
	}

	// Images
	$imgs = $document->getElementsByTagName("img");
	foreach ($imgs as $img) {
		$filename = $img->getAttribute("src");
		if (!filter_var($filename, FILTER_VALIDATE_URL)) {
			$filename = $dir . $filename;
		}
		$mime = mime_content_type($filename);
		$data = base64_encode(file_get_contents($filename));
		$img->setAttribute("src", "data:$mime;base64,$data");
	}

	$stripped = preg_replace('#>\s+<#s', '><', $document->saveHTML());
	printf("%s\n", $stripped);
	exit(SUCCESS);