find_classless_anchors.php

<?php
$str = '
	<a href="?class=blah">foo</a>
	<a href=""><em>foo</em></a>
	<a href="bar">Foo</a>
	<a href="bar" style="blah" class="foo">Foo</a>
	<a href="bar" class="foo">Foo</a>
	<a class="foo" href="bar">Foo</a>
	<a class="foo">Foo</a>

	<a href=\'?class=blah\'>foo</a>
	<a href=\'\'><em>foo</em></a>
	<a href=\'bar\'>Foo</a>
	<a href=\'bar\' style=\'blah\' class=\'foo\'>Foo</a>
	<a href=\'bar\' class=\'foo\'>Foo</a>
	<a class=\'foo\' href=\'bar\'>Foo</a>
	<a class=\'foo\'>Foo</a>

	<a href=?class=blah>foo</a>
	<a href=><em>foo</em></a>
	<a href=bar>Foo</a>
	<a href=bar style=blah class=foo>Foo</a>
	<a href=bar class=foo>Foo</a>
	<a class=foo href=bar>Foo</a>
	<a class=foo>Foo</a>

';

preg_match_all('~<a(\s+(?!class=)([^=]+)=(("[^"]*")|(\'[^\']*\')|([^\s>]*)))*?>(.*?)</a>~i', $str, $matches);

var_dump($matches[0]);


// MY REGEX FU IS THE STRONGEST!